I have the Palm Centro and it is a joke. It is really uncomfortable to hold, the buttons are oddly shaped, the operating system is poorly layed out and difficult to use, the screen is very low quality, and even though it is a "smartphone", it sucks because most applications are not compatible with The Centro. So i think you should go with the propel, i Know samsung always makes high-quality products.
I have a palm centro and I love it, I had several phones before this one and I was skeptical when I got this one. It took me a few days to get used to the phone but its very simple and I personally thinks its very convenient. If you get a memory card for it you can store tons of songs and pics in it, its easy to text on it, and I have dropped it several times and it still works!