Swedish tank destroyers

[Duke]

Is there any functional difference between the swedish atgm based tank destroyers? (one gets a 20mm gun and weaker missiles but other then that...)

[AttackerCat]

I presume you're referring to the UDES and the Pbv 302 (BILL)?
The Pbv is a different, more modern chassis with a better engine and mobility (~19hp/ton vs ~14hp/ton), plus yes the 20mm autocannon.

[Kay]

The BILL isn't a "weaker missile", it's a different kind of missile. It's an overfly top attack missile so it flies above your crosshairs (and target) and detonates above it, sending its penetrator down through the roof of your target.

IIRC the other two are just normal TOW missile carriers