The worst thing to do is to leave a question like this open for these tech heads here to answer....Everyone is going to give you what they think is the best device in their opinion. I would suggest you narrow it down to even 3 devices then make a sensible decision from there....from the 2 devices you had quoted above I would go with the Samsung Blackjack2. Its running WM and that will give you far more options especially with desktop integration (windows pc), and corporate integration. Plus great application support. HV recommended the TyTN or the TyTN 2, yes I will concur with his recommendations those are excellent devices, also due to the fact that you said you wanted a PDA. I am assuming that the PDA functions and the Internet will be more your primary use than the actual phone. (but they are still great phones though)....
To Know, Dare, Will and Keep Silent.