Hardcovers look better but are more expensive and sometimes harder to read. Softcovers are cheaper and efficient.
You said it all. Most of the stuff I own are softcovers, merely because they're cheaper and easier to handle while reading. Hardcovers extra weight and annoying slip covers just make them cumbersome to read, though hardcovers do look better. However, I buy my trades based on the story within, not the appearance on the outside, but more importantly, the cheaper price of softcovers. Also, uniformity goes a long way...all my Ultimate trades are softcovers (well, most anyway, with the exception of a few that my LCS owner screwed up on ordering hc instead of sc), as are my Y trades, etc.
This applies to novels as well. I can't justify spending $25-$30 on a hardcover novel when I can buy the softcover for $7 later on, and the softcover will end up taking up less space on the shelf.
Yeah, softcovers all the way.