I don't know much about using winches to load timber (I just yank what needs to be yanked with the truck), but I've been an offroad nut for years and have a lot of experience with winches in that arena. I would recommend running dual batts if you plan on doing lots of regular, extended winching. Even with relatively little load on the line, elec. winches still draw a lot of juice. If you are planning on running one on the trailer or rear end of the truck, I'd use the heaviest cables I could get to reduce voltage drop (which will burn up winch motors) which will occur over the long distance. I use 0 gauge to my 12K Warn, and it's front mounted. Another handy trick I picked up is the use of a choke cable connected to the carb/TB that can be used to set the motor at a nice high idle (about 1500-2000 RPM) while winching to get the alt. cranking and the voltage up. Standard alternators actually put out very little at idle speed, and if the engine is at normal idle, most of the amperage will come straight out of the battery(ies).
For the purposes of pulling logs, I would imagine a 6 or 8K planetary would be plenty and would be the fastest (line speed) simple option. A PTO winch would be really sweet since you would have all the power you'd ever need, any speed you want, and no electrical hassles, but that would be complex, expensive, and certainly not portable.
I am not a fan of receiver mounted winches having seen their mounts tweak and twist as a result of shock loading (which you may well encounter if a big log takes an unexpected roll or something) or even just a decent side-pull. Plus, if you're talking about a class III hitch, the receiver is probably rated at no more than 6K at best (straight pull) and is not designed for side loading. I know a lot of people run 'em, but that is MHO.
Edit: If you do decide on an electric and you really want the Caddy winch for your application, go with a Warn 8274. They are the fastest standard winch Warn sells, they are indestructible, and they hold something like 150' of 5/16" cable (wire rope). However, they are $$$. Otherwise I'd go with a plain old M6000. They're cheap, compact, relatively fast, and probably more than strong enough for your purposes.