I agree it has to be gut feeling - only you know really what will suit your children better.
DS1 is starting school in September and his school is not small - the intake is 70 so they have 2 classes of 30 and another that is mixed with the eldest of that intake and the youngest of the previous intake.
Personally I prefer this option as it's more hustle and bustle, there are a wider range of kids to connect with. For me, a very small school would just feel claustrophobic - can't really explain why but it's just a personal thing. I'm quite an extrovert though and like lots of things going on around me and ds1 is very similar - he's not shy and gets on with everyone (mothers of the kids at nursery, all different ages, come up to me and say 'my ds/dd loves Thomas').
Apart from this though, of course there were all the other things to consider and despite having classes of 30 they have excellent results year on year, have a huge plot so brilliant playing fields/playground, school meals freshly prepared every day on-site, a great IT suite, links with similar primaries in Italy, France and Spain, links with the local hockey/lacrosse club.....
There are other schools locally that are much smaller that also have consistently great results but have tiny plots of land so no playing fields, less sports and extracurricular activities and I'm very keen that the boys have lots of opportunities to do different things and have lots of fun - it's not about getting straight A's for me.
So, it depends on your kids personalities and where you place your priorities I guess but again, it is very much down to a gut feel about a school when you visit it.
Good luck! Hope I've not rambled too much