I will start by saying I have never done an engine swap, but all the engines you mentioned, I would have to say the 3.4 would be easiest. It will bolt to either the auto or 5 speed (you will need a 3.4 from a 5 speed donor if you want to run a 5 speed) and you can buy a wiring harness to get the thing running. Disadvantage is supposedly you need a 2" body lift.

The 7M-GTE is most desireable for many reasons. An inline-6 is one of only three engine designs that is inherently balanced due to its design (the rotary and a V12 are the others), the engine itself is much simpler than a "V" design, the engine is *way* overbuilt to handle lots of boost (oil squirters to cool the bottoms of the pistons, two oil coolers, dual knock sensors, etc.) and makes far more power in stock trim than any of the engines you mentioned. 232 hp and 254 lb. feet of torque. I have a MKIII Supra with this motor and IT DOES make tons of torque down low. Add a full 3" exhaust and a K&N air filter and two washers under the wastegate and you'll be making over 300 hp and somewhere around 335 ft lbs. (Search for my other threads about modifying this engine.)

Disadvantage is you need to be able to do some custom work yourself. You will likely need to run electric fans due to space issues and you'll need to find a place to mount the intercooler. (Seems to me it might fit behind an IFS skid plate.) Torque the cylinder head bolts from 58 ft. lbs to 72 ft. lbs and have fun!

BTW, a friend of mine has a 4.3 in their pickup and is installing one in his rock buggy. After helping me work on the Supra (and especially after driving it) he wishes he would have bought a 7M.