I personally would say go with the Mbox. The software is very well developed and mature, easy to use, and full featured. The midi features have come a long way, and Digi keeps improving them over time. Since it sounds like you are intending to use the Mbox for recording your band and not heavy midi sequencing, the pro audio orientation of ProTools suits your goals. Finally, compatibility is an issue in my opinion, and you'll find it very easy to trade session files if they are recorded in ProTools. I don't personally know anyone using Tracktion professionally, or Cubase LE for that matter, although I do know a ton of people using ProTools and/or Digital Performer.
I have an Mbox and
a Digi 002r. I started with an Mbox and went to the 002r because I need more tracks out (up to 18 on the 002r). Both boxes work great, and the software is tops for recording audio. Digi includes a bunch of software plugins as well, so you have those to work with right out of the box.
As far as latency, there is a no latency monitoring feature on the Mbox, but that is without internal fx. If you want to apply the internal fx while listening back, then you have to route the signal through the interface. There will be some latency in that case. But that is true of *any* of these units that are being recommended to you. It is the nature of the beast: there will latency if you run your audio through the hardware, into the software, and then back out again. This will happen with any and all DAW's. You control the amount of latency by setting a buffer in the software. How low you can set it depends on the speed of your computer.
So again, in my opinion Digi's Mbox/ProTools is a great choice.