Depends on the fleet
If you are talking about going against hot boats with high tech gear, then break out the big bucks because there is no other way to compete and forget the roller. If you are dealing with older, cruising-oriented boats then you can give a decent account of yourselves with a new dacron roller from a good loft. Freshness and condition mean everything within the parameters of what the material can offer. The law of diminishing returns kicks in once you go past dacron - you can gain 10% but at double the price and half the life. So it becomes a question of how fast you can afford to go, with each increment becoming more and more expensive. I bought a good dacron 150 roller three years ago, have raced it about 50 times since then (short 3 to 7 mi races, mostly), have taken good care of it, and it still shapes well and gets us near the front. If you have much light air, go for a sacrificial UV strip rather than the heavier Sunbrella, as it will make a big difference in leech shape in light air.