I've been running a couple of 525SS faucets on my side by side for about a year with no problems. Decided to add a third tap and went with the 630SS. They're both front sealing faucets which is important if you don't want to deal with sticking faucets. I do notice a slight difference in "feel". The 630SS seems to have a shorter throw and doesn't feel quite as smooth as the 525SS. It's not really an issue, just feels different. They're both quality faucets and will serve you well. I have heard of a few people that have had leaking issues with the 525, so you may want to consider that as well.
When I did my build, I to had that question. I asked my friendly tap room and they used the 525SS taps. I also priced the parts piece by piece but ended up with going with KegConnection. They saved me some money and they were great to deal with. They were the best for freight costs.
I like the perlick 525ss myself, but regardless of what you choose...I would make sure everything is stainless. I have seen many chrome faucets and shanks with the brass showing from wear, which means you drank the coating. no thanks!
I looked at the reviews and the 525ss seemed near the top of the list for a good price. I asked for, and got one tap for Christmas. Then I saw that Perlick was replacing the 525ss with the 630ss so I decided to buy two 525's more before they were gone. They had actually gone down in price where I bought them. When they arrived there were one of each for the 525 price. They are slightly different in looks but not enough that I was disappointed. As previously mentioned the 630 has a more mechanical feel and has a slightly shorter throw. I have had no issues with either. I would recommend either.
I love my Perlick 525ss. They are well built and are easily dissembled to clean and rebuild. They are very classy looking as well. I bought mine used for a very good price but I won't think twice about buying my next one at full price. I just got lucky because they came with my keezer. There is one upgrade I made to mine which made them smoother. Mine had plastic bearing cups which I replaced with stainless ones. I heard the plastic ones can make them leak too. I bought all the o-rings and bearing cups from keg outlet which was very cheap.