I'm looking to replace the one on my machine, and I can't decide if I should go with a spouted like I have now, or try a bottomless. I don't really make two espressos at once, so the double spout is not a necessity for me.
Bottomless is easier to clean and lets you see more of what is happening with your shot - you can tell if your tamp/etc is even based on where the coffee first comes through. More of a mess though if you have shoot-through.
I think bottomless is also more desirable/seen as an upgrade if you ever sell the machine.