You need to decide some things first. What is your budget and how much space do you have? Do you want a machine on a frame or a sit down machine? There are advertisements in every quilt magazine for longarm and midarm machines. Plus you can use your favorite search engine and find tons and tons of information on both.
You can quilt straight lines with any sewing machine you can put a walking foot on. You can free motion quilt on a lot of machines too. I have stuffed a full size quilt thru a regular sewing machine so I know it can be done.
You may also want to look at the regular machines with the larger throat areas. I think there are several brands now with 9 or 10 inch throats. Some of those can also be used on frames.