[fyshstykr]

I agree with Bonefish, see if you can cast the 2 lines for each rod, most fly shops will have a few reels loaded with various wts and tapers.
The heavier the line, the better the rod will load, but you also need to look at the action of the rod, a faster action rod will handle the heavier line easier than a softer action rod generally.

I would also suggest trying different line tapers, I've found that newbies have an easier time casting a w/f line than a d/t, nothing against a d/t line as it has a time and place, but the w/f line seems a bit easier when teaching someone to cast.
J.