Note the date of these sites, as software changes frequently!
All the major Qualitative software packages have implemented an exchange file format allowing you to transfer your project from one software to another. We highly recommend using a software that supports the project exchange format OR that is open-source.
Online: These make it easier to collaborate with others and offer per-month pricing, (~$10-20/month), good for shorter projects
These do not seem to have any advantages over the above at this time, unless simplicity is the primary goal or a perpetual license (for $75-200) is desired.