I've really enjoyed the Firm workouts. I have the 4-pack of workouts that came with the Transfirmer (the larger rectangle version, not the original square version) and then also the 4-pack that came with the weight bar a few years back. The general workouts consist of Cardio, Abs, one that's heavily strength and then one that I can't remember. But the routines are different from pack to pack, so I didn't get 2 packs of the same workouts. I used to use them all the time, but now use them to supplement in for a "change-up" in my routine. (My personal-trainer-best-friend and I both love any of the Firm workouts with Alli Del Rio...she's awesome!!). But really, you can't go wrong with any of them.
The best way to keep the effectiveness of any workout is to keep your muscles confused. Therefore, don't do the exact same thing every day. Gotta keep it mixed up! I recommend 2-3 days of cardio and 2-ish days of strength/core work per week. If you workout 3 days a week, make 2 of them cardio and 1 strength. Muscles build a lot of calories, even at rest...so the more muscles you build, the more calories you'll burn! But if you can fit in more days of workouts, go for it :)