It sort of depends on what you're looking for, but as far as polished product goes, I think Sportsline is fantastic. It's very customizable and gives a good medium for posting messages and stories to taunt your leaguemates. The full price is $150 or so... I paid $120 for my leagues buying a month ahead of time and googling for a discount code.
But the only websites I've used have been Yahoo, ESPN, Sportsline, and rotowire (which absolutely sucks). So there may be better out there. But everyone who I've played with on Sportsline (over four different leagues, one of which has been around for five years) suggests staying on Sportsline whenever we're starting a new league and thinking of trying something else.
Also, as far as keeper league: I would vote you start from scratch. Particularly if you decided to do a keeper league now and not before you did this year's draft. And I'd look seriously into doing an auction draft. It's the best way to make drafts fair, but particularly keeper leagues, where if you get one of the first two picks you have a dominant position for a number of years if you just keep the draft snake-style.