Hardware-wise, the N900 wins because it's better built and has more and better features.
Software-wise, both are good but the N900/Maemo/MeeGo wins again because it's ultimately more capable and much more open than WebOS.

Plus, as ysss said, Palm is all but dead. They've let it be known they're actively seeking buyers. Palm has only 2 options:
1. Be bought out, most likely by a Chinese company.
2. Go bankrupt, more likely than #1 because Palm would be cheaper to acquire then and could be bought in pieces. The corpse will be picked over for WebOS or the Palm name, though those have a pretty limited value. Patent rights are the only thing of solid value Palm owns anymore.

Well, it could be a lot of things, plenty of reasons the iPhone sucks. #1 reason for me is I don't want Emperor Jobs to own my @$$.