Hi Kim, welcome back. I'm just going to chime in on a two-piece system that I use. You can look up the part numbers on my profile if you like; everything is there.
Let me put it this way: you know when you grab an apple and your fingers are completely around the apple? Completely? Visualize that for a second. Now, obviously, you must have a little bulge like we all do. Of course, I think it's pretty natural. Okay, take that same apple and try to wrap a napkin around it. Yeah, a tissue napkin.
Which would have a better grip? I think the first one, and that's the Sensi Flip starfish design.
It makes perfect sense to me, at least. You got this five-finger design basically attached to my little bulge there of that little bump, as opposed to four corners with a square mounting plate. And the other thing, you know that cleaning you do? You don't have to do that with a two-piece. You can rotate the two-piece if it's drainable. You can rotate it from a downward position, which I would say would be 6:00, and rotate it to a 12 position to put some water in there to soften up whatever has accumulated. Return to 6, and drain. I do this usually before I go to sleep. It's a really big help. So with the two-piece, and particularly this type, I have no complaints, and I try to recommend it to as many people as possible because it's a good idea. There are many things you can do with a two-piece. It's the flexibility that you don't have with a one-piece. You don't have it, and you have to keep changing it. I believe one-piece does come with drainable pouches, so that's cool. Also, one-piece is slimmer, more trimline, so you might want to think about that too. So there are pros and cons.
For me, the two-piece is the best.