Both are good devices actually, but for different uses.
iPad is nice for home usage. Easy internet browsing on large screen, effective virtual keyboard and many new applications are coming which take advantage of its screen size. I have even lately seen an iPad DJ turntable application which was really cool to play with.
Galaxy Tab is full of functionality including camera, GPS etc. Lightweight. Very suitable to carry around. Total freedom from iTunes and conversions. So, it is for maximum mobility.
Overall, I would suggest buying both (if you can afford)