I have done both- and both are great! But very different styles:
CE is 5 days a week - 3 days of lifting, 2 days of cardio (dvds provided). For lifting, you lift slow heavy weights with very few reps - forcing yourself to have good form and your muscles to fatigue. Every month the workouts change out - first month getting used to lifting heavy and building muscle, 2nd month lifting really really heavy and the 3rd month dynamic lifting to shred you into lean muscle. There is also some great ab tapes. Diet is key with Chalean - you have to stick with the program and trust it to see results.
Pump is a little different. It is a little more flexible with the schedule - every other day is a "walk" day which basically means do any form of cardio you want. They have a les mils cardio package sold separately which is awesome and I love (1 step workout, 1 sport workout and 1 combat boxing workout). On these days, you do the ab tape - which is quite tough!
The workouts on lifting days for Pump are different too- the idea with pump is reps reps reps. You squat/lunge/lift more than you thought humanly possible. It is choreographed to music though, so you really don't even notice.
So 2 programs with very different techniques/philosophies but the same goal

Also, CE is 3 days lifting (each 35min) 1 day long cardio (45min) and 1 day short cardio (30min) - every month new dvds, but the lengths are the same.
Pump starts out with 2 short 20 and 35min workouts for month 1 with the ab tape (15min). Then month 2 is the 35min workout and a 45min workout. Then month 3 the lifting workouts are each 1 hour long. The cardio package dvds if you want it them are 30-45min.
I would recommend "you tubing" the 2 workouts and taking a look at the style of each. I was unsure of Pump for a long time because I was such a Chalean fan. Then I found a few videos of it on you tube and changed my mind. So glad I did too because I love it just as much!
good luck with your choice!
Rachael