Neither of the first two NES Contra's are all that difficult. I've beat Super C with one life a bunch of times. The trouble I run into with Contra is in the Energy Zone (Stage 6?). For whatever reason, I can never get through the beams consistently.
That single stage wipes out half a dozen of my men (give or take), which means I generally have to use the 30-lives code on account of one friggin' level. Other than that minor setback, I have the first Contra down pat and don't lose a single life in any of the other stages.