Assuming they are set up correctly, just about all offer a huge improvement in off road performance. I think you can generally caragorize EFI systems as either throttle body or port injection, with the latter divided between batch fired and full sequential. There is little difference between batch fired and full sequential at higher rpm, but the sequential does have an advantage at low rpm. About the only pit fall for the throttle body systems is that you can still have fuel/air separation issues because you still have a carb type manifold. The port injection does away with this problem. TBI systems are reasonably cheap while you can spend a whole lot of $ on a port injection system. Both will work.
One set-up I rarely see discussed here, perhaps due to cost, is Edelbrock's multi-point (port) fuel injection system. I have it, and it's the way to go. Expect to pay over $2500 as compared to Howell's throttle body system for a little over $1000. Alternately, you can do the "junkyard throttle body conversion" as discussed many times on other threads here.
The price bumped a bit about a year or two ago when the ProFlo went full sequential. I don't think the change probably incured any additional manufacturing costs doing so but guess we need to support those few companies still making things in USA. I bought the 35000 ProFlo II for the 3B for $2800 from my local engine builder (Internal Combustion Machine). A lot of money but it is still the most flexible system I have seen. There is a learning curve but there is just about nothing it will not do (except maybe pass the smog guys). After a simmering 35 year battle with Holleys and complete rejection of the Edelbrock carbs, it is pure, unadulterated pleasure. Don't like something? Just toggle down a few menus and change it-on the fly.
That depends on what else you have done to it. What it will do is eliminate any hacks or studders, even upside down (at least until it runs out of fuel because the tank pickup is sucking air), and allow you to maximize the performance however the engine is set up. You probably will get the biggest kick if you have at least an RV type cam and some decent compression as most versions flow pretty well. Again, a lot of money. Would I buy another? Absolutely! Most fun I have ever had playing with the tunning. No gas to drain to change jets, no cams, needles, or springs to change, no gaskets to replace, no advance curves to alter-just a few keystrokes and it is all done.
__________________ '81 Scrambler w/ FI 360 AMC, 33x12.50 BFG M/T's, 5" of lift, ARB'd Dana 44's F & R, Dana 300 clocked & twin sticked w/4:1, Warn XD9000i, etc...
2002 Grand Cherokee Limited, 2008 Overland Grand Cherokee, a 1976 CJ-7 in pieces and 3 more off-brand 4x4s............... John N