Don't know about Rotowire's baseball provider, but I used it last season for football and it was awful. It had some neat features such as an automated Free Agent Auction Bidding each week for waivers, but the interface was the worst of the four that I've ever tried (Sportsline, ESPN, Yahoo, and Rotowire). I'd have to see something pretty impressive out of them to use them again.
I've run a handful of leagues on Sportsline the past few years and won't run a baseball league anywhere else (of the ones that I've tried).
Primary reasons for liking CBS:
(1) Player pool is basically everyone in the majors and minors who you ever would want to draft or take for the future;
(2) Relatedly, all their major league and minor league stats are there for you to check out;
(3) Friendly interface for league (lets you post polls and stories/articles with uploaded pictures as well as upload your team logo's):
(4) and most importantly for baseball, lets you use and combine basically every statistic that is tracked. For football, I don't care so much since football scoring is so vanilla. But I find the standard 5x5 stats for baseball to be bad in measuring player values and anything that Sportsline tracks (which is basically everything) you can use and combine in any formula you can come up with. In one of my leagues, I have the calculation for Runs Created per game as a trackable stat... didn't end up using it for scoring, but it's possible to do.
0-3 to 4-3. Worst choke in the history of baseball. Enough said.