IGX

I've tried a few. My reviews:

Nike+ Ipod app
Pros-- good on battery life; easy to play tunes; easily uploadable to Nike+ website; free; don't have to run other Ipod services to use it and the Nano will easily fit in your pocket.
Cons-- you need to set your pace with it. It can be +/- 20% if you don't. Not great for rucking or trail running (especially because your pace changes).

Accupedo app
Pros-- Decent on battery life; default setting runs all the time, so you can track how much activity you do throughout the day (this can be changed to only run between certain times a day); free (has a pay version I didn't pay for)
Cons-- same as nike+ but +/- 10%; used on your phone.

Endomondo app
Pros-- uses GPS so tracking is the most accurate; can be set for more activity styles than the others (running, hiking, walking, -- it has other options like fitness walking that I haven't tried); maps your route and suggests routes others use (for $2 it will track changes in pace and altitude changes-- there are other options I haven't paid for); free; tracking pace at various parts of the route (with $2 upgrade)
Cons-- hits battery hard (if you're not using it, manually stop it from running); used on your phone.

Notes-- Accuracy based on fixed routes. All of them do calorie counts, which can be adjusted for sex, age, and bodyweight. I don't like having to run with a phone on me, so I always list that as a con. There are other apps/tools out there, but I haven't tried them.

Recommendations (from the three):
Running-- I prefer Nike+, largely because I like the option of listening to music and don't want to carry my phone with me. AFAIK there are better running tools out there, but I haven't tried them.
Activity tracking-- Accupedo is good for this, only works if you're carrying your phone (obviously). Would be nice for goal setting if you're trying to walk a certain distance daily.
Route mapping-- Endomondo hands down if you have consistent GPS signal. Nike+ if you're running a consistent pace or off a pace count in a more remote area.
Hiking/rucking-- in areas without cell service, Nike+ as long as you've factored in your pace count prior to starting. In areas where you're confident in having consistent cell service and aren't going for more than a three hours without a recharge, Endomondo hands down.