I prefer the look of an unlined board, but I prefer playing a lined fretless for accuracy. Maybe it's a crutch, or maybe it's just a tool to make playing the instrument in a better fashion, everyone has his or her opinion on that, but I don't think it can be argued that lines are an impediment to playing the instrument well. Either way, as others have touched on, having a good ear is key. If you have a shop in your area that has a fretless or two, go check them out and monkey around with one for awhile. The Squier VM Jazz fretless is a fine place to start for the money, but there are other budget fretlesses out there.
It's not for everyone, but in my opinion playing fretless opens a whole new world of expressive playing. And if you need to sound like a fretted? You actually can by playing with accuracy and without vibrato. Fretless is FUN!