either a 3 or a 5 wt, depending on the size of the fish you are going to catch. 3 wt for 12 inch or smaller, 5 wt for fish bigger that 12 inches. a 5 wt casts longer, and 3 wts are more precise. (Generally.)

In your case I like the 5 or 6wt, sense
you will be backpacking I would suggest a
4pc rod with a hard tube to carry it in.
You said you were new to the sport and
and are probably overwhelmed with all the
different kinds of rods there are, not to mention all the actions.
Do you have a bass pro or cabellas near you, if you do the people in the fly dept. are very knoledgable and can help you, if one of those are not available feel free to contact me I will help all I can.
Alex is right, a 3wt is more precise but with you being a newcomer I think a 5 or 6wt will be more forgiving of your casting tecnique,especially if you get a
med/fast action and I suggest a 8ft rod
unless you will be fishing very tight streams then I would go go shorter.
You didn't mention a reel or line, I figure you will be fishing for trout so get a center taper line for a more delicate presentation.
Most important get out in the backyard and
practice your casting!!! dont forget to
practice the roll cast.
If you dont have anyone to teach you to cast, there are alot of videos on youtube
that can show you how.
Remember those trout are very easy to spook so you have lay that fly down lightly and doing that takes lots of practice so hit that backyard when you get your rod.
any questions you have I will try to answer, my email is adodger69@yahoo.com
Roger

I just picked up a St.Croix Triumph Combo. Its 4 wt 2 piece 7'6 rod. also came with a semi okay reel fully equipted. Now since your hicking you will want a 4 piece rod or more which will be easier to handle while hiking. I went with a 4wt, this means you can go up one wt size, so if i wanted i could go with a 5 wt. Youwill like the st. croix triumph being a beginer. Gander Mountian carries them, also cabelas. Check it out.