It is like trying to compare a Hollywood blockbuster with an indie documentary, or a symphony orchestra with a busker. This year’s RIBA Stirling prize for the best building in the the country sees the £19bn Elizabeth line and the 67-acre regeneration of King’s Cross go head to head with a little row of council houses and a refurbished farmyard in Dorset. The annual architecture gong is always a case of apples and oranges, but the disparity in scale and cost has never been more extreme than on this year’s shortlist. Joining the diverse bunch are also two fiendishly complex transformations of existing buildings, the Victorian National Portrait Gallery and the postwar Park Hill housing estate in Sheffield. How on earth will the judges decide? Of the two big beasts, the Elizabeth line might clinch it. It is the one bit of UK transport infrastructure that makes you feel like you’re living in the 21st-century, a bright, spacious world of airy tunnels and sleek sliding doors. It is the part below ground that’s up for the prize, namely the “line-wide” design by Grimshaw architects and Atkins engineers, who have created a streamlined universe of white concrete panelling, incorporating up-lighting by Equation, and elegant signage totems by Maynard. The result is a futuristic environment that gives commuters the feeling they’re walking the sci-fi corridors of Stanley Kubrick’s spaceship in 2001: A Space Odyssey. If there’s a complaint, it’s that all the stations are alike. There’s none of the quirky character of the Central line’s mosaic and enamel platform decorations, or the architectural flourishes of the Jubilee line, which help to make the stops easily identifiable at speed from a crowded carriage. The Lizzie line is an efficient wonder, but it’s also a monotonous blur of beige. The King’s Cross development, masterplanned by Allies and Morrison and Porphyrios Associates, takes the opposite approach. This is a rich buffet of more than 30 different architects working across 20 new streets and 10 new squares, on former railway lands. It is a well-judged marriage of old and new, seeing the bricky relics of industry transformed into an arts university, shopping mall and assorted dining concepts, alongside new homes and offices. The architects were given relatively free rein, with the one proviso that they “respect” each other, and the results are a mixed bunch. There’s the gargantuan ground-scraper of Google’s new headquarters, by Thomas Heatherwick and Bjarke Ingels, a fun tower of bouncing brick arches by Alison Brooks, and an imposing neoclassical pile by Porphyrios. The public spaces are more successful than the buildings, chiefly the phenomenally popular fountain-studded Granary Square. The plan is more sophisticated than most other regeneration projects of its size, but, like the slightly soulless world emerging on the Olympic site, it feels as if some grit is missing. And, as a sizable chunk of city, made by numerous hands, is it too big to win the prize? Perhaps it was packaged together because no single building here would warrant the award. Weighing in at a tiny fraction of the size of King’s Cross is Chowdhury Walk, a little lane of houses in east London’s Hackney, developed by the local council. Designed by young architects Al-Jawad Pike, it is a model of infill development, replacing a former row of garages and parking spaces with 11 new homes, seven of which are social rented, the four others sold at market price to help pay for the rest. The houses are staggered at an angle, reducing overlooking and forming a sawtooth profile along the street, where each home enjoys a recessed porch framed by raised granite planters. The energy-efficient houses are built of cross-laminated timber, with triple glazing and solar panels on the roof, massively reducing residents’ fuel bills. The project is full of neat details that elevate it above the everyday, like a jaunty upside-down arched window on the end of the terrace, and cobbled paving that gives way to pools of planting along the pedestrianised street. It is a lesson in how to make ordinary housing feel special – and it should be commonplace. But the cost of this level of quality makes it unlikely to be replicable. Budgetary constraints were less of a concern for the intricate £41.3m revamp of the National Portrait Gallery, by Jamie Fobert Architects and conservation specialists Purcell. It is a regal fantasy of bespoke silk-lined walls, polished marble terrazzo floors and exquisite walnut display cases. But the real ingenuity is mostly hidden. A delicate process of keyhole surgery, making strategic cuts and connections, saw 20% more space conjured from the existing warren of rooms. Formerly blocked windows were opened up, letting light flood in, classrooms were carved out below ground, spilling on to a new sunken terrace, and a new entrance was boldly sliced through the listed stone facade. A sloping public forecourt elegantly deals with access, doing away with the previous “accessible” entrance down a side alley, and putting all visitors on the same level. The project has utterly transformed the place, in ways that are sometimes imperceptible. Rethinking accessibility was also a central concern in Wraxall Yard, the careful conversion of a dairy farm in Dorchester into a community space, educational smallholding and group of holiday lets, by Clementine Blakemore Architects. Working with the Centre for Accessible Environments, the designers have crafted a place where the subtle manipulation of the landscape avoids the need for separate routes, ramps and handrails for wheelchair users, while the interiors incorporate sinks with integrated grab-handles, rise-and-fall worktops and ceiling hoists, without feeling institutional. As much of the existing buildings were retained as possible, with new additions built using reclaimed materials and natural, low-carbon products, like cork and wood fibre insulation. The result is a poetic place that helps to get everyone – from the isolated elderly to young people with mental health issues -engaged in the countryside. Finally comes the second phase of a colossal project that first graced the Stirling shortlist over a decade ago. The reinvention of the much-maligned Park Hill housing estate, which marches across the hilltops above Sheffield like a concrete cliff, has been struggling along for 20 years. Each phase of its transformation reflects the time it was conceived, and the latest, by Mikhail Riches – winners of the 2019 Stirling prize for their pioneering low-energy social housing in Norwich – is the best so far. It has seen 195 flats reborn, preserving most of the original fabric, while vastly improving its energy efficiency. The brickwork has been cleaned, revealing a gradient from terracotta at the base, through ochre, to pale mustard yellow bricks at the top floor. Windows are bigger and more thermally efficient, while external walls have been insulated with coloured render, in heathery shades inspired by the nearby Peak District. One argument against it is that, in this particular phase, all the homes are private, representing the council’s shortsighted transfer of a public asset into the hands of a developer, Urban Splash. (Previous and forthcoming phases include 20% affordable housing.) But the lessons are here for braver councils elsewhere to take note and do similar things themselves. As the project with the most widely applicable tools for tackling one of the biggest challenges facing the country – namely, the upgrade, rather than demolition, of postwar housing estates to handle the climate emergency – Park Hill would be a worthy winner. But is this essay in insulation sexy enough to seduce the judges? The winner of the RIBA Stirling prize 2024 will be announced live in London on 16 October.