I think "best" is somewhat subjective, but a few of the front runners:
The new HP Ipaq h5450 supposedly has the most beatiful screen, and has everything but the kitchen sink - 400 Mhz X-scale processor, 64 megs ram, 48 megs ROM, 802.11b, bluetooth, fingerprint reader, removeable battery, and IR port powerfull enough (and w/ software) to use as a remote for home electronics, and an SD expansion slot. $699, available 12-09-02.
The Toshiba e740 has built in Wifi, and has dual expansion slots (SD and CF). No built in wifi, but 400mhz, 64/32 ram/rom, and is much cheaper (~450 online).
The Dell Axim X5 is only $299, has 400 Mhz, 64/48 ram rom, and dual expansion slots, but no integrated anything. Still, at that price, you could probably buy a wifi CF card, 256 megs of expansion, and a keyboard for less than the cost of the HP.
My $.02