Well, Sam is pretty much the best, let's be quite honest here. By Tolkien's own word, Frodo becomes a bit "rarified" by his great suffering--a bit distant. Bilbo, Pippin and Merry don't "air time" necessary for fuller character development that Sam gets. Who else provides that unique mix of loyalty, fearlessness, and humor, as well as the weaknesses we can all so identify with, but Sam?
Still, all these hobbits are great. Off the cuff, speaking of the sort of "second tier" hobbits, I personally like the Gaffer, Sam's dad. The nut doesn't fall far from the tree.