Burris Fullfield II 3-9x40. For the money one of the clearest scopes. Maybe even one of the 2-7x35s for the .30-30 since you probably won't be stretching it out that far. I have a 3-9 on my .25WSSM and I love the thing. Strong, bright, clear, and the ballistic plex reticle is awesome. http://www.burrisoptics.com/fullfield.html
I use at least a 40mm on anything I hunt with for the light gathering. Put the best you can afford on a muzzleloader if you run 150gr loads.They will ruin a cheapy after a few shots. you never mentioned your budget
Generally speaking, for a .30-30 levergun, I like a small light scope with a low end magnification in the 1.0-2.0 range, and high end magnification in the 4 to 7 range, and an objective lens no larger than 32 or maybe 36.
This is the scope I'd buy right now if scoping pretty much any short or medium range rifle, if you can afford it: