Re: How to select fly line?
Your fly line should last longer than 6 mos. Especially this time of year when I assume you haven't been out every day. Try cleaning your fly line with mild soap and warm water. Gently. rinse and dry. You can also "treat" it with a little bit of fly floatant (Gink, etc) if necessary. I sometimes clean/treat mine with Ray Bergman's fly floatant formula consisting of a mix of paraffin wax and lighter fluid. You can google that one.
If you do need a new line for some reason, you usually get what you pay for. Buy what your budget allows. Color doesn't really matter, but I like pale ones like peach or light green. If you have a 5/6 rod, you generally would want a WF-6 line for that. However, that matching the line number to the rod number is not always the best match. Its a good starting point though, and works for most rods. Some rods work better with one weight heavier line. If you like the line weight you have now, stay with it.
Make it a habit to clean and dry your line at home every few trips, or every few weeks if you're going regularly. It will last much longer and float better.