There's no one single best workout.
You have to focus on different muscle groups, if you only do crunches then you'll have rockin' abs, but little/no arms or legs or pecs or shoulders etc.
What I did when I wanted to get into shape 4 months ago, is I got a weight lifting set for my birthday.
I do (you may want to google some of these) bench presses, dead lifts, military presses, crunches, push ups (you don't have to do both push ups and bench presses, they work the same muscle groups), psuedo push ups, crunches, hold the plank position, and leg lifts. Of course this isn't getting all the muscle groups, but it gets a good chunk of them (I think)
After a while I changed it up, doing one handed push ups and hand stand push ups (with the wall) in place of regular push ups, elevated psuedo push ups, so on.
Also most people recommend, you can do weight lifting on one day (call them A days), and cardio (running/swimming/etc) on the next day (B days) and just make your schedule ABABABABABABABABABAetc. You don't have to stick to it, I take days off. Sometimes I do something like ABABABABABAB RR ABABABABABABAB.
I'm no work out master, I don't know much I admit, but doing this I have noticed really good results. I've lost 26 pounds (I was overweight for my age/height and I did seriously cut down on junk food though) and have gained noticable muscle.
Also, if you do start weight lifting, find the amount you can lift only once, no more and no less. For me this is 170 pounds for deadlifting/benchpressing and 130 with military presses.
When you're exercising, you want to do 3 reps of 60-80% of your maximum that you can only do once, so for me I bench/deadlift 140 pounds, and military press 100 pounds. I do three reps of each
Also, from what I've been told, if you work on the lower end of the spectrum (60%) it's how you toned, i.e. ripped, and if you work on the higher end of the spectrum (80%), it's how you build more strength.
Also, a good weight lifting workout lasts ~45 minutes, keep that in mind.
Last thing, when you weight lift, make sure you do each work out until you seriously cannot do a single one more. You'll be insanely sore when you first start, but after a while you won't get as sore or sometimes you don't get sore at all.