They are both great guns. Recoil springs are very cheap and I have not had a problem with my Gen 3 Glock 22. I am the armorer for my department and we have only had to replace one recoil spring out of the 10 pistols. I prefer the feel of the Gen 3 but if I was buying new would go for the Gen 4 for the back strap alone.
The only differance is the 2nd Gen has no finger grooves and the 3rd does... the polymer guide rods can be troublesome. they had a problem with the recoil springs on the 4th Gen .....I am a Glock aholic. Feel free to pm me with any questions concerning Glocks. My suggestion is get a stainless steel guide rod, they for around $40 .....G27
G22 Gen III bought off my good friend which was his duty carry. He never had an issue nor have I.
As for the gen4 spring issue I don't think it was as widespread as one may think. Glock took ownership and replaced the springs in a recall correct. A bnib should have no issue.