The 09 4 cylinder is a completely different engine than the pre 2001 4 cylinders. Quite a substantial power increase. You won't feel under powered with either truck and both engines are rock solid reliable. If you're never gonna use the 4x4 or tow I'd definitely go with the 2009. Mine gets 25+mpg on the highway so its an excellent commuter truck and is no slouch for power. When you consider the extra weight of the 4x4 both trucks are probably comparable in power/speed but the 4 cylinder will always win in MPGs.
The 4.0 is an old school simple pushrod engine. Very reliable and simple to work on.
The 2.3 is much more sophisticated and less easy to work on but proven extremely reliable (its the same engine in the new 2019/2020 rangers without the turbocharger).
I've never owned a 4.0 ohv truck but have worked on them and think they are good motors. I own a 2.3 so 3 things I know first hand to watch out for...
#1 the PCV valve needs to be changed fairly often (ford says every 12,000 miles) and it is a major pain in the butt to replace until you get good at it. You need to remove the wheel and inner fender and then it's still quite a feat of stretching and squeezing.
#2 there is a coolant hose on the back of the engine, its not common for that hose to fail BUT if it does, you need to remove the transmission to replace it. I always keep dye in my coolant to check for leaks back there.
#3 it runs on the verge of a high compression engine so it uses a knock sensor to tame it under heavy load. If you ever haul anything or drive through big hill country you'll notice a power loss unless you run higher octane gas.
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