Also fed up with the crap stock app, I got on here and tried Textra first.. It's good, clean, but lacking a couple of features I really want. First that comes to mind is message count option; I prefer this to be shown in my conversation list.
I ended up with Chomp, and so far it's working great.. with a ton of customization, which I like also! No trouble with MMS; in fact it displayed images out of my MMS's that the stock client would never display.. Old stuff in conversations, not just new messages.