So, it really depends on your lifestyle and preferences.
I see someone recommended P90X3. I love the Beachbody workouts, and the 30 minute ones are great.
But. (you knew there was going to be one, right?)
I am a social animal when it comes to exercise. The thing I like about DVDs is that is has the "feel" of a class, and it forces me to pay attention and work out - compared to when I'm just doing a weight workout at home by myself, I just can't wait until it's over and I get lazy.
I would MUCH prefer to work out in a group, and I LOVE the gym. (I have 2 memberships it's that bad!) I added the YMCA membership after my second triathlon. I learned to swim in my 40's and really enjoy it now. And it's good for my joints. My prior gym had a pool, but only 2 lanes and 1/2 a length. It got hard to count laps when you are up to 50-60. I swim 30 laps in a standard 25-yd pool now.
THAT'S why I keep my Y membership (and we also take the boys). Yes, I could bike to work more, etc. etc. but I like to SWIM. And I'm going to fess up - during cold/flu season, I'm a bit of a germophobe, and sometimes in January I'm lucky to go 2x the whole month (but in September it's more like 4x a week).
I get my group fitness in the pool too - same 7 people every time I go, we all have our favorite lanes. My lane buddy is David. Single guy in his 50's. I'm faster than he is, but he's been speeding up!