Things in favor of iPad:
Optimized iOS out of the box; Thousands of apps optimized for Tablet
Smooth and Amazing Web Browsing/Gaming Experience
Things in favor of Tab:
More RAM!!
More mod-ability (via community support)
Cameras
Can be used as a phone (yea yea I know )
The biggest difference between the two, though, is
PORTABILITY!
If you want a bigger screen to casually browse when home, get the iPad hands-down!
If portability and light-weight is what you are looking for (especially to surf the web on the go), go for Tab (only because it is now selling for cheap)!
In the end, both are Gen-1 tablets and are already outdated with the launch of iPad 2 (and Tab 2 release around the corner). So I would invest in something which has a better chance of being future proof and IMO, that would be the Tab since there is a very high chance of it getting Honeycomb unofficially/officially! However, as is the case with all Android vs iOS devices, if you don't want to mess around/tinker with the tablet, get the iPad for it's sheer OOTB usability! For Tab, you will need to flash custom firmwares/mess with the internals to get a smooth experience!