Both probably have comparable performance (68K code on fast '040 vs PPC code on slow PPC!), and aren't the most reliable of portables made, so I'd go with whatever looks the best in terms of case plastics, motherboard condition, etc. Make sure you resolder the DC jack as most have snapped off or are loose due to their small fragile size.

You can overclock the PB5300 to 117Mhz fairly easily:

http://www.alksoft.com/5300_overclock.html

The colour screen should be a straight swap. The passive matrix colour screen is terrible though, only get the active matrix display if making the swap.

JB