Switching apps?

Okay, so I had posted my workout through my iPhone app on Friday, and got a comment or two that the calories burned seemed low to them (my walking partner had mentioned this before, as well).  So I decided to do a little investigating on my own, and here's what I found:

• My current iPhone app says that 35 minutes of walking at a 3.5mph pace burned 176 calories.
• I checked an online calculator, and it says that the same time, same pace would burn 296 calories.

WOW - that's a pretty big difference.  I'm beginning to wonder if I need to switch apps in order to get a good idea of the calories I'm burning.

So here's my question: what iPhone apps out there do you think are good for this?  My walking partner suggested RunKeeper Pro, and so far I like what I see, but I thought I'd see if anyone out there has any other suggestions before I drop $10 on it.  (Before you suggest I go for the free version, I would like the option of setting intervals, so that when I get further along, I can start incorporating some jogging into my workouts, along the lines of the Couch-to-5K program.)

Thanks in advance for the suggestions!!