Dollar for dollar? 2.3 turbo. Unless you've got a 5.0 donor car sitting nearby to grab all of the 5.0 specific parts (and there's a bunch of 'em).
For the most part, if you get a complete 2.3t including the computer and VAM, It drops right in with a little intake/exhaust plumbing, A little ECU harness wiring and some engine harness wiring. That's a vague description at best but you get the general idea.
Being just as vague, here's what you're looking at to do a 5.0 swap.
Fuel line rerouting, rear end swap, rear brake line rerouting, engine wiring harness swap, computer swap, tachometer swap, if the 4cyl car in question is an automatic you're looking at a trans, crossmember and driveshaft, if it's a 5spd, you'll only need a 5.0 spec 5spd. You'll need a complete exhaust system, different coolant recovery tank, do you have A/C? You'll be swapping the drier, lines and compressor. The 4cyl has lighter front springs, so you'll probably want to change those too. You'll be adding a little weight up front and those small 4cyl brakes may not get you stopped like they used to so you'll be looking for some 5.0 spindles, rotors and calipers, or if you decide to go 5 lug, you'll be hunting a set of 94 and later spindles, hubs, calipers, and rotors.
Depending on the smog Nazis in your area, you may have some issues getting it to pass visual with 4 more cylinders than the VIN says it's supposed to have.
I had the same dilemma you've got now when I first got my '91. I've got an '88 Turbo Coupe motor on the stand now that's waiting to be rebuilt. As soon as I can scrounge up the rest of the funds to get the small parts and the cyl head done, I'll be dropping it in my '91. After talking to a couple of local guys who talked me out of dropping an EFI 514 in it
I found this site and Turboford, and that's all I needed I was hooked on the 2.3T. All my V8 hot rod, pro street, show car buddies think my little project is cool and can't wait to see it finished.