I would say that 30 Day Shred was the best because I really understand the moves and have done them in settings where a coach showed me how to do them correctly. I actually still feel the most sore on days when I do 30 Day Shred level 1 because I can do it well.

Extreme Shed and Shred has 2 parts. She asks you to consider doing both back to back, if you do, then it is probably very effective. Thus far I have done part 1 only and it does not feel as difficult. I think it will be good to mix it in there just for variety. I love 30DS but can get bored, so I mix in others. I also run, bike, rollerblad on days that I don't do her videos.

Here are my thoughts on her videos:

30 day shred, ripped in 30, and extreme shed are pretty similar (the last one being a bit longer) and my favorites. The have the mix of cardio, strength, abs
NMTZ is great for days that I don't do cardio. It is really hard but I just do 25 minutes at a time. It is intense strength training.
BFBM is too long of cardio in a dvd for me, I'd rather run, bike, swim, skate on a day I'm going to do that much cardio.
6 pack abs was too hard for me, only tried it once and didn't finish.
Buns of steel, or something like that, I didn't buy because I think it will be like 6 pack abs
Yoga meltdown is pretty good but I hardly do it becaue I am not too familiar with yoga and feel like I have to look at the tv too much

I have Extreme Shed and Shred and found that I dont really like it as much as all of her other videos. Its a fusion workout so she she combines kickboxing with martial arts and yoga which is great but when she switches it up it gets my heart rate down too much so Im not burning as many calories. Some parts are challenging, like the traveling burpees but I feel like I get more out of 30 day shred.

And I have done BOTH of shed and shred back to back for 90 minutes and still felt like it wasnt that great of a DVD as her others are.

Hope that helps.