I've got a JCB 800 roller and its been fine. Sure, compaction needs more passes to get it down, but it will do it. And there's been plenty of times where a 120 would have been too big for me. Kubota engine, simple enough machines, should give me a lifetimes use really.
The one to get if you can is the 1m wide ones, a lot more stable but still on the smaller 80 chassis, but they are a lot rarer and of course you have the same force over a larger area so again, a few more passes, but for track maintenance, your only scratching the surface up to remove potholes etc so an 800 would put it back down ok anyway. Its the deeper stuff they struggle with.
I'd rather have to do more passes than not be able to use it because its too big, so an 800 works well for me. And if your only doing it once a year, an hours extra time (maybe even less depending on the area) isn't exactly the biggest negative against the storage space and cost to buy.
The other good thing with the JCB rollers is there are sometimes ex Jewsons or Travis Perkins ones that come up at auction with very little hours on and you can get a bargain. Bomag's seem to make strong money and I don't think they are as good as they used to be. Hamm's are good, but love an electrical issue on the dashboard! And Ammann's are terrible for electrics - avoid!