There are numerous designs of Twelves and some favour particular crew weights, conditions or types of sailing water. The factors to consider when selecting the design for you are:
The typical crew weight for a National 12 is 17 to 23 stone. Certain designs are generally considered better suited to crews at either the lighter or heavier end of this range, however people successfully sail all sorts of designs with various crew weights. If you are at the lighter end the designs which you might want to consider are
If you are at the heavier end you may want to consider
As a general rule some designs of 12 are more suited to either inland sailing where you need maximum manoeuvrability or sea sailing where speed in a straight line is important.
For inland sailing, rounded hull shapes with fine bows and a good amount of rocker helps the manoeuvrability and pointing. Good examples are:
For sea sailing, deep veed bows, wide decks and wide transom sections with less rocker will help the boat power through chop and plane downwind. Good examples are:
If you want a design that will do both pretty well there are a number of all-rounders, for example the Feeling Foolish, Crusader or Design 8
Vintage and classic boats are fine for club sailing. It is worth noting that the handicap rating (Portsmouth Yardstick) for the National 12 has changed since these designs were built. The Association has produced a set of recommended handicaps for the older boats which you can suggest to your club.
Open meeting sailing
The more recent single bottom boats are known as "Admirals Cup" boats. There are separate prizes at most open meetings and the Championships for these types of Twelves so you don't have to own the latest designs to have competitive sailing and win prizes.
To seriously campaign for the top slot at the Championships, you will need an double-bottomed self-draining design, as these are stiffer and lighter. A carbon rig would be helpful but is not a pre-requisite. Carbon and glass foam sandwich hulls are equally competitive. Don't get too hung up on the designs, helm and crew performance will no doubt be the deciding factor.
Now you know what consider have a look at the detailed design descriptions