I run the SCT Livewire which is both a monitor and stores custom tunes. I run tunes from Innovative Diesel and like them. There are others such as Elite and Matt at Gearhead among others that I have read good remarks about. My Livewire stores multiple tunes and you can switch them anytime (except on the go).
I have read that canned tunes are not only bad on the engine (blow headgaskets) but can cause premature trans failure. I have the tow +40hp tune, stock without EGR, street and extreme street. I run and tow (up to 10K) with the street tune and get identical mileage that I did before when it was bone stock but it IS indeed a different truck. I occasional try the extreme street but it has a lot more power on tap and has a more aggressive exhaust tone and too much power if I have to loan out the truck. The monitor function is really flexible because you can choose from many layouts and you can pick which parameter you want to monitor and where on the layout.
Here's a rundown on tuners
https://www.youtube.com/watch?v=KWJ-l_udw7s
Here's a rundown on the Livewire
https://www.youtube.com/watch?v=GXNYOdox48g