I agree with everyone else here... with $50 to start with, FT $1.25 sit n goes are your best value. The 9-handed tourneys get you $4 for first place, and they're fairly easy to consistently beat. Just make sure you're playing small pot poker and minimizing your losses if you think you're beat, until you get into top 3. Those games only take 30-45 minutes max, so just practice patience, and you should fair off well.
The $2.25 18-handed sit n' goes are great to take a stab with once you've gotten your BR to about $70 and want to take a stab at making a leap in prize money. $14 goes to first place here. Again, if you've been comfortable taking down the $1.25 SNG's, this should be a really easy game to adapt to, as you won't notice any difference in the caliber of player. These games though may go to about 1.5 hours, and you'll find it easy to at least cash consistently enough to make a profit off of this.
I think the $1-$3 SNG's are a great range to play within when your BR is within $50-$200 (depending on the risk you're willing to take), and you'll find that the profit you can make at these levels are more lucrative than the profits you can make in the cash ring games (.05/.10 and .10/.25) in the same time period. One major suckout in a ring game at these levels (which happen often with ultra-aggressive donkologists) can cripple your whole buy-in, whereas with a SNG, you can easily take on the damage of a major cooler without hurting your BR. The amount of action and play you get gives you a greater opportunity to adapt, learn, improve, and elevate your game to real money
If you've been playing with play money up until this point, it's very wise to get as much hands and volume in without risking your whole roll, and SNGs will help you accomplish this.
Good luck at the tables.