Don't waste your time and money on anything other than a Stihl.
Some suggestions, without knowing where your located, and at what altitude. I would not get anything smaller than a MS-362 using a 20" bar. It's a professional series saw, which will last you a lifetime if you take care of it. You'll spend more money on a pro saw, but where that comes in handy is it will have a better power to weight ratio, thus less tiring on your body if you're out there cutting for a full day. You can go with a non-Pro saw to save money, but you will have to pay for the savings in time and energy.
If you want to go with a 16" bar, look for a used 024-AVS. My Dad bought the one I have new back in the early 80's. It still runs as if new, and is my main limbing saw, but has a power to weight ratio that can't be beat by nothing but my MS-440 Magnum.
Don't use fuel with Ethanol. If you can't buy Premium fuel without that added crap, then spend the extra bucks and buy cans of True-Fuel, which is a premix that you can buy that's either 40:1 or 50:1 mix ratio. The new Stihl's are designed to use the 50:1 mix. Some WalMarts carry it, and most Stihl dealers are now carrying it in addition to Ace Hardware.
As mentioned above, the Chisel tooth chains are great cutters, but if you have the tendency of getting the tip of the bar/chain in the dirt, cutting dirty wood or brush, I would suggest the RM chains. The RM chains stay sharper much longer
Chains; don't buy safety chains (green painted link), they don't cut worth a damn. They're designed to reduce kick-back, and you'll need to learn to operate the saw safely before attempting any serious work anyway. If you buy a new saw, ask that they give you a non-safety chain, and buy a spare also. ...and a file for sharpening.
Keep the chain sharp, immediately touch it up after hitting dirt or the ground. If you touch it up every third or fourth use, it will go a long time before requiring a professional sharpening.
Keep your air filter clean of chips and sawdust. This will allow the saw to run better. The new Stihl's have a redesigned air box filter (they copied Husky) and stays cleaner much longer.
Dump the old fuel out of the tank before using it for the first time that season.
Keep the saw in the shade when it's not running, while your working. The new saws don't release the pressure from expanding fuel when sitting in the hot sun, and causes vapor licks that sometimes make the saw difficult to start again. I usually open the fuel cap, and release the pressure before trying to start it again.
Buy safety chaps, I had a recoiling limb push my saw into my knee, and lucky it was a glancing blow with minor cuts. Since then, I've been saved several times - life and limb wearing my safety chaps. It's stops the chain instantly if it hits your legs.