I think the C4 is the easiest vette I have worked on. I had 3 C3s but I like the hood access on the C4. My C4 is 300,000 miles old, so I replaced basically everything on the car. The engine was never removed, but I was able to replace the oil pump and rod bearing twice. You can remove the oil pan easily. You can remove the starter without having to remove the exhaust as it is on my C5. It is also easier to remove the tranny on a C4 than on a C5. On a C5 you need to remove torque tube, all rear suspension, and diff. It is also easier to replace wheel bearing on the C4. On the front C5 bearing, you need a special tool to remove the lower A-Arm.
I find the C4 interior easier than the C3. It is also a bit easier to remove the cluster and dash panel on the C4 than it is on the C5. Doors panel are easier to remove on the C5. Seats are the same.
Anyway, it is fun to work on Corvettes. The only differences between C3, 4 & 5 is the following: On C3 you do not need the instruction manual. On the C4, the manual is a couple of inches tick. On the C5, the books are 5 inches high.