Whatever you end up doing, it should be measurable. By that I mean you should be able to tell the good it is doing your body otherwise you will get demotivated.
Essentially, you should aim to be lean - for a lady that means around 16-20% body fat. Athletic woman are very lean at around 12-15% body fat. Obviously the less fat you are carrying around the quicker you will be.
The other measurable is heart rate - which measures how "conditioned" your heart (which is just a muscle really) is. The more conditioned your heart, the fitter you are and the harder/longer you can perform for. Your resting heart rate should be sub-70 at least, but in the 50s for someone looking to be athletic. Heart rate is also important during excercise, as too low a heart rate and you are wasting your time and too high a heart rate and you are damaging your heart. I see so many people trying to get fit/lose weight and they burn themselves for 5 minutes doing nothing but harm as their heart rate is far too high, when they should be doing say 20 minutes of intense but safe training at an appropriate heart rate.
The interval training mentioned above is very good for paintball, as it teaches your body to perform, recover, perform, recover etc etc.