There are arguments on both sides as to what looks better.If either one isn't done right- they both look terrible. Let's start with plastic sails. You must cut these out very straight and slightly sand the edges so they are not jagged and nothing looks worse than a shiny sail. When's the last time you saw shiny cloth? But time after time these plastic sails have a sheen on them. Especially with plastic you have to try and hide the fact that its plastic and fool the eye and one of those tricks is to spray your sail after weathering with an acrylic dead flat. Most modelers poke a hole in the corner of the sail so as to tie it off when rigging the ship which is fine so long as it doesn't tear. A better way is to glue rigging string around the perimeter of the back side of the sail and leave "loops" in the corners so as to tie them off when rigging. Another complaint with plastic is the sails just hang there- there is no billow to the sail. You can glue 26GA wire to the very edge(next to the string) with CA and hold it in place with alligator clips until the glue dries and then bend it to your desired billow effect. Paint with a light cream acrylic color then highlight the patches and tears with different colors of pastels. You can also get a textured effect with some Rust Oleum texture paint. If you lay down the sail and spray the textured paint in short bursts at 24" away (or further) you'll get a great texture. Experiment with a piece of plastic to get a desired effect. I've experimented with 3 different plastic kits with sails- The Constitution, Hellers Victory and Le Soleil. The Constitution and Le Soleil have excellent embossed sails but the Victory's look terrible so a texture of some kind would look good on these sails. Reef points can be added only a string at a time poked through holes in the reef band and tied. With weathering,pastels,and billowing a plastic sail can look just like the real thing.
Cloth sails can be soaked in tea to get varying degrees of weathering on them,best to try out a handkerchief first for best results. All cloth sails that I've seen are folded over on the edges and provide a perfect channel to "thread" like a needle 26GA wire through on each side of the sail and curl a tiny loop in the wire on the top and bottom for purposes of tying off for rigging and to billow the sails.Reef points can be installed in the same manner as the plastic sails. Wrinkles can be taken out by spraying a small amount of water on sails and slightly shaking them. It takes patience and experimentation to get the results that you want but it pays off in the long run.