Use both. What worked well for me is to use a jet for the biomes nearby (all the KSC biomes, the shore, grassland, highlands, desert, I think there's even a patch of tundra nearby KSC). Make a two-seater jet with all the science equipment you got, take Jeb and Bob (a scientist) and start collecting science biome by biome. Works like a charm. Edit: so use the scientist to reset the instruments when landed, works much more efficiently than by dropping disposable science pods (though that sounds kinda cool). Edit2: also remember that you can drive jets just fine, which is especially good when visiting all KSC biomes. However, to reach the badlands and pole biomes by early-career jet is not really feasible: it takes ages to fly there. So for these ones you could build a rocket, maybe even one with a small jet strapped on top. But to be honest I have not bothered for the few science points that this would net me. Much better by then to fly to the mun or minmus.