Now I will respond lol
Touchscreen you can use anything you want on it (finger, pen or any other body part (your palm for example can interfere with signing something on a normal touchscreen). Touchscreen models (on the CF-30) offer 1000 nit screens (nit = measure of brightness - the higher the brighter)
Digitizer is basically a tablet PC and has the tablet PC input pen in order to use it (can't use your finger for example)... Good for signing digital papers for example. These models usually only go up to 500 nits (half that of the touchscreen model).
Personally if you don't need a fully rugged model - For example if you don't foresee dropping it from 3+ feet, or don't plan on going swimming with it lol I would consider a CF-52 as those are the most powerfully toughbooks you can get that still have a handle on them (my buddy just picked up one for $1370 for a 2.26GHz model here: viewtopic.php?f=10&t=100
). Obviously no-one would forsee dropping a computer from 3+ feet but consider what you are using it for. I for example have a fully rugged model because I'm in the the IT industry and frequently use this computer while on a ladder taking notes. I also like doing a lot of outdoorsy stuff like camping and can't risk it getting destroyed while getting wet from being in a tent or from being rained on lol. (Yes I take my toughbook with EVERYWHERE mostly for music and finding out things on the internet with the Sprint card while on the go)
If you want a fully rugged model I would recommend the CF-30. They are expensive as hell but work so damn good.
The CF-19's are CONSIDERBLY smaller than the 30's and the 52's and have great battery life as well - they have an 80% sized keyboard - so keep that in mind if you plan on typing lots of papers that that might suck (at least for me it would).
At this point I would try to stay away from a CF-29 or CF-18 only because they are much much older (the 30's and 19's have been out for more than 3 years now) and are much slower because they aren't dual core CPU's. I had a CF-29 for MANY years before upgrading to a CF-30 and don't regret it AT ALL because the CF-30 is sooooo much faster!!
As for the keyboard - I personally have an emissive backlit keyboard so it can be used at night (it doesn't take any more battery life at all) and because it's easy to type on. S.C.R.E.W the rubber backlit ones - nice because they are sealed from sand and debrees etc... but once again - ask yourself - will you take your computer into the sand pit?? lol
Well that is one page. Any more specific questions just ask!