Your best saws have more than one speed, can use blades of various widths and has a throat that's large enough to cut parts large enough to build your models.
My first saw was a 7.5" B&D, not a real good choice as it couldn't handle anything over around 4-5" nor did it have an actual miter guage or fence. I moved up to a Craftsman 14" and have never looked back. Stay away from the three wheel saws as they are harder to get to track properly and, according to other's posts, they tend to be harder on the blades than a two wheel types. Just got to thinking, get something with roller guides as they are a good upgrade over guide blocks and are easier on the blade as well. Having vacuum ports is a bonus since it will decrease the sawdust flying around in the air during use