I use Android pay in preference to contactless card payments now - I've pretty much stopped using cash.
Android pay works fine and has the added benefit that if your phone is unlocked you can make a contactless payment of up to £100, while the card/phone locked payment is limited to £30. I find that higher limit somewhat more useful. I would to know of some way to remote nuke the phone though, just in case it gets nicked. Hmm, actually since I access company email on it, the remote nuke policy is in place which is about the only benefit doing that brings.
It's not surprising that Samsung Pay hasn't gained traction, given how appalling they are at updating their phones.
Now that Touchwiz has less of the "aarrgghh my eyes are bleeding" look about it, for me It's less about updates and more about me too apps. Duplicated mail, browser and all sorts of other stuff including another payment app? But that's another story.
Samsung pay currently supports my bank and one of my cards but as far as I can see, there's no additional value add so no reason to use it over Google's version...