As with all ecommerce queries, you ask which is best and you will get 50 different opinions, many from peeps who have a vested interest in the result.
What I would suggest AND what I ask prospects BEFORE I accept a project OF ANY TYPE IS....
What do you want your store/site to do, what are the 'key features' for you, what do you see as vital customer interactions outside of the norm (if any), what kind of support will you need after sales, where are you based (UK etc) and where is the support based (usually India LOL) and so on....
when this information is gleamed, you can then go ahead and state which suits best.
There are so many small time carts, white labelled carts (children of OS such as osc etc) and big time carts such as X Cart, Actinic etc so you must make sure it suits you first and foremost.
Sorry to chime in guys but how many times do I read the same theme and then see 100 posts, mine is best this is best etc without fully gauging what the full story is....
IMHO to answer the OP's question...
The one that suits your needs best
Regards
Daren
(ps, to help prove my point, check the number of posts from the majority of people offering services ;-))