Agree with wowza, the envelope ones are the easiest. I found the others very fiddly, too many poppers in odd places.
Most vests do not need to be pulled over a babies head. They have envelope necks so that they can be pulled down around the baby. Just make sure they have sleeves/necks like the ones in this link:
+1 never had any issues with the envelope ones. I look for tops with envelope necks too
We got them for DS in Tesco when he was a baby
Didnt have these for DS but decided they would have been a great thing when I saw them in Tesco when he was a few months old. Went there to buy them for DD almost a year ago, and couldn't find them in any Tesco I looked in.
I bought two long sleeved from Next and two short sleeved from punkin patch in Blanchardstown. Each set of two were about €10 which makes them significantly dearer than normal ones but I think they were worth it in those early days.