Hmmm....
For size AND definition, you have to go with bodybuilding because true powerlifting packs on fat which hides definition. However, I've also heard that when powerlifter takes the time to cut off the fat, he's more impressive than most bodybuilders.
Start with bodybuilding because you can get results with realistic amounts of weight. I've thought about pushing for more powerlifting, but you have to really use a spotter with heavy weights (something I don't have) and your joints need to be able to handle it (I have tendency for arthritis--some workouts leave me sore).
In ANY training routine, you have to vary your load to keep the muscle from adapting. I'm still using the MuscleNow program, and here's the basic 6-week training deal.
Week 1 -- 8-11 reps, 2 sets, 2 min rest
Week 2-3 -- 4-7 reps, 3 sets, 1.5 min rest
Week 4 -- 8-11 reps, 4 sets, 1 min rest
Week 5-6 -- 4-7 reps, 5 sets, 1 min rest
(repeat)
As you can see, on weeks of less sets, you'd push harder on the sets you do. Likewise, when you do more sets, you tend to go to less reps, so you can keep pushing. The muscle never gets to adapt and stop growing.
Results vary, but it's not unusual if you have 2-3 cycles of good training to see you start say at 50 lb on one thing, stay that way for 6 weeks, yet the next Week 1 you can easily do 55 or 60. I've found growth is then limited by what you can get genetically and how much you eat. I recently broke 100 on my flat bench (with dumbbells
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), but now that I'm cutting, I'm back down to 85-90. Once I start bulking again, I'll likely get to 100 and start pushing for 105.
Also, I won't go into it here, but you must get your diet squared away. Proper protien/carb balance at each meal in your day is key to burning fat and building muscle. It's a fairly accurate science where diet comes in, so you can't neglect it.