i think the quality of the blade is more important than the handle. as long as the blades are interchangeable, choose the handle that's most comfortable for your hand. i buy only generic blades, they fit all my brands of handles, and i'm satisfied. the money i save let's me throw them away a leeetle bit sooner, but really not too much sooner. they hold up pretty well.
the problem is that the handles come blister packed and you don't get to try them on. not every place lets you open them or has a sample. i know that joann's doesn't let you return anything once it's opened, so if it's not comfortable, too bad.
i think starting with the 45's is most sensible. it lets you do wide curves (not tight ones) and of course straight lines. the 18''s let you do tighter curves but they wear out faster because they turn so many more times. and the 60's are really only good for straight lines. in the end you have to decide how you'll use it. you can always add another if there ends up being a size you wish you had.