93-94 were the odd-ball years. The 4.0 ohv heads were weaker and prone to cracking. 95 heads were redesigned and much stronger, as well as the trucks getting the new style dash, as well as switching over to a standardized OBD2 computer system. 4.0 sohc engines from their development in 96 through 01 had their own startup of issues, mainly only being the chain tensioners, but still a good motor. All the 3.0 Vulcan motors are pretty reliable of all years, but are not known for power(they are a dog). All 2.3/2.5 motors are dead reliable, but again, are for economy only. My personal choice, would be anything newer than 96. In 97, creature comforts started appearing more and more in these trucks (pw & pdl) as well as other features like bucket seats and so on. 98 started getting extended cab doors that open, which were called 3 and 4 door trucks. Also in 98, 4wd models had a new front suspension design, made for a better ride, but gave you more moving parts and more expensive lift kits. Depending on your needs and wants, will determine which year to buy. 93-94 I would stay away from, only cause those are the oddball years with unique wiring harnesses and they are getting old and harder to find in the junkyards for parts. Plus for the same price you can get a 95 with newer looks and amneties...
SVT
I have to disagree on a number of points here...
I don't know where you got they're "odd-balls", but '93 & '94 were probably the most reliable years ever in their day. For one thing they don't have the sticky door pins that cause the dome light to stay on and the dinger on some years to blare away incessantly while you're trying to drive ('95 for sure, possibly '96 & '97 too). They also don't have windshield wipers with a "phantom" mode. As for the wiring, I'm not sure how common it is to have issues with wiring unless it's been butchered up at some point...

The vast majority of parts (interior and chassis/drivetrain) are common from '90-'94.
I also have not heard that many reports of 4.0L heads cracking as you say (certainly not like I have 2.9L heads). I do know the newer heads are better for performance however.
Also FWIW, the SOHC motors weren't used in Rangers until '01, though the chain tensioner issues still hadn't been resolved until even a few years after that ('04 I think). From what I know about it, it's more of a noise issue than anything ('97 was 1st year for the SOHC in Explorers).
To the OP,
As for what year to buy, it really depends on what you want from it.
If you're looking for a 2WD, I say buy as late as you can find/afford. All of them are pretty good.
If you want a 4WD to modify into a trail rig, '93-'97 with the Twin-Beam front suspension is what you want (much more rugged, and easier/cheaper to lift/modify).
If you just want a foul-weather driver (4WD) that you don't plan to modify the suspension on, I would again say buy as new as you can find/afford (but try to avoid the '98-'00 models with the PVH auto hubs).
Can you swap the 95+ knuckle out onto a 94 axle?
I'd love to trash the pin setup and have dual piston calipers.
Yes, you can put the '95-'97 axle ends (knuckles/spindles/brakes) onto the earlier trucks w/D35 axle.