There's more channels on Freesat than Freeview, but there is a few channels on Freeview that are hidden behind Skys paywall so not available on Freesat (Yesterday, Pick TV, Quest, Dave) if they're important to you.
I have both, but if i could only have one or the other i'd pick Freesat everytime.
Freesat's PQ is marginally better, it has potential for growth/adding more channels because it isn't bandwidth deprived like Freeview.
Freesat also has more red button/interactive streams than Freeview (though they maybe cut as part of BBCs cost cutting/to fall in line with FV), all BBC/ITV regions are available (which is handy for me being a Londoner living in the N.E who likes access to regional programming).
Freesat will also be gettiing the the 24 SD/HD Olympic streams, which aren't possible on FV because of it's bandwidth constraints...