Celtic, I don't know. I think all Christian religions observe communion whether its once a week or once a month...

I haven't found too many fundamental differences in the denominations of Christianity. We all seem to be on the same page regarding the Holy Trinity, the ordinance of Baptism (whether sprinkling as an infant or the adult decision to be baptized after accepting Christ), the observance of Easter, Christmas, etc.

I would feel comfortable in any protestant or Catholic church. As a matter of fact, I've regularly attended all sorts of flavors of Christianity. Catholicism seems to be very ritualistic and more concerned about legalism, but with a refreshing devotion to their belief system, and from that end of the spectrum you can go all the way through to the other end and everything in between to Episcopal or Methodist which seem to have accepted just about anything to keep their denomination afloat. (personal observation) I have a cousin who is a Methodist pastor and he and his wife are trying to bring their denomination back to a more traditional belief system.

Then there are some who claim to be Christian religions which, in fact, are not at all. I won't name those but they come door to door more often than most and are mostly works based. They think only a few people are going to Heaven and they want to make sure its them by going door to door and working real hard.

Mostly I think it just depends on the individual, how they were raised, what their level of relationship to Christ is, how close they are to Him, their tastes in music, worship, and other factors but all good.