Contra 4 is good, but I prefer Contra for the NES. I'm not sure which is harder. I never really got into the other Contra games (mostly due to either not having money or not really knowing they existed back then). Contra NES is one of my all-time favorite games probably due to the extremely high difficulty challenge.
I can beat Contra 4 on easy, and with a lot of continues I can probably make it through normal but the game is hard. I switched to the challenges, and then sort of put it to the side and haven't really played my DS much other than getting a new game and beating it then putting the DS back down.
If you can beat the challenges, you can play the original Contra on NES but it isn't the same, but it would give you an idea of what it is like.
Ultimately, the game comes down to memorizing where all the bad guys are and when they will show up and just run through the stage real fast while shooting the entire time.








