For sarcoplasmic hypertrophy, leg press is documented to be the most effective. Done in proper form, regular squats are going to be next to the top of the list. Collegiate exercise science departments study this stuff at length, so...listen to the science and not your local trainer.
When I was in my 20's and biked a lot, I had 28" thighs at 5'5". Nowadays, at 53, and scared to jump on the bike in DFW traffic, I'm lucky if my things are at 26".
I torn my left hamstring doing standing leg curls a year ago, and it's slowed me up, some. I'm FINALLY getting it mostly rehabbed, but, it's been an arduous process. I let my quads get too tight, and hyperextended my hamstring, and tore it. Sucks..because stiff leg deads are something I was very good at I had several medical folks tell me that I had the thickest erectors they had ever seen on anyone my height (35 years of deadlifts will do that).I split legs, because it's 2/3 of your lean body mass and it takes lots of calories, and cardiac function to do them in earnest.
When you develop power, and size, through your legs, you are stronger in cardio, intensity, and become a calorie burning machine.
I do like so, by day:
1. Back and bis
2. Chest and tris
6. Rest / cardio / missed part
It's important to allow adequate recovery time. If you are NOT juiced, your testosterone can approach near zero if you exercise too hard, too often, too long (that's the attraction of "the juice."). Time off is when you make gains. Sarcoplasmic hypertrophy is a completely different thing than muscular hypertrophy. It's important not to confuse the two.
It's also important to eat. If you don't eat an abundance of calories, you have put yourself on a plan for failure. You need your base caloric requirements, plus 600kcal per hour working out plus 600kcal, daily...to make optimal gains. Don't bother with crap like aminos. Spend your money on food.
Here's quad day from two weeks ago (I've been home with the flu.)
1. 6 set of leg press, (includes two warm up sets). 8 to 25 reps. All the way down; all the way up.
2. 4 sets of front squats. 8 to 20 reps. All the way down; all the way up.
3. 4 sets of hack squats. Same thing.
4. 6 sets of independent motion leg extensions.
Sit on your legs. When you can do that...you're loose enough in your quads. do other stretches, too, post workout..not before. Stretch everything, every time you're at the gym. Flexibility is key, especially as we get older.
1. 6 sets of stiff leg dead lifts. Go easy because you want to be able to walk.
2. 4 sets of step ups / lunges (usually step ups...lunges grind my knees)
3. 6 set of independent motion leg curls, or sometimes even more...Think leg bicep. All these in the same 8 to 20 rep range.
I rotate through abs, forearms, and calves with each workout. A lot of times, I'll put abs in as agonist to hamstrings.
Stretch, post workout...
A muscle contracts in only one way. No need for esoteric exercise. Work the muscle through its full range of motion. I wouldn't squat with super heavy weight to the floor, because of the way it loads the bursa in your knees, but, other than that, a fully stretched, full range of motion, is critical to maximum gains, and minimal injury.
Do stairs if you can handle it, or work up to HIIT on the stairs.
You'll get big, lean, vascular legs.
Discovery and Nat Geo has done a few really good programs about The Human Machine, and AAS. (The Incredible Human Machine, and Science of Steriods)