the only atomizers you can use without an adapter is the 510 and 306. the reo and majority of mods have whats called a "native 510" connection (where you screw you cartos and atties in)
510s are easier for the new user...but i personally jumped right into the 306s as they produce the most vapor and have the most similar type draw to an actual cigarette...it will take a little practicr though in learning how to not flood it.
IMO, id go with the Ciscos at
Avid Vaper : Electronic Cigarettes, E-Liquid and Accessories or Ikenvape (but theyre always sold out) only because they dont come with primer...which can be a pain in the ... for a new user.
Generally, the lower the number resistance in ohms, the warmer the vape and the more vapor, but might be at loss of some flavor. 1.5ohm = hottest, 2.0+ohm cooler. they say 1.5s for tobaccos, and 2.0s for the fruity, flavored stuff. id suggest going with 1.8ohm as its in the middle. i like my vapor, so i go with 1.5s.
if you decide on the 306s, youtube how to "dewick" the atomizer. its a common practice for 306s...not everyone does it, but the majority do.
hope this helps