Cannondale's integrated and propietary designs are cool performance and looks wise... but indeed, its too much of a hassle replacing or upgrading, I wouldn't get a Canny for that reason alone, they are fine bikes but I can't see myself riding a headshox or lefty with peace on my mind but you know, that's just me, try a Cannondale yourself.
The Marzocchi MZ III is a poor fork, nothing special and I'd like the J3 on the base Rockhopper more because of lockout alone, jump to disc brakes and the Tora suspension is worth it and you are getting a better deal component for money with the Rockhopper Comp than with the Rockhopper base model. Konas are also amazing but their sub 1000$ hardtails all come with MZ3 forks, hydro brakes might even that out but BB5s are great anyways and very adjustable, between Kona and Specialized... I'd pick Specialized component wise and fit-wise (better said I picked specialized over kona
), but you really need to know if the Kona or Specialized fits better, otherwise components won't matter but if you are basing your choice on components alone... get the Rockhopper Comp.
As for the Trek 6700, its a great bike, very light, great components but its also more expensive and do keep in mind the Trek is a very XC oriented bike and if you are looking at more aggresive riding styles the Kona and Specialized will serve you better.