I actually came here to suggest something along this line, but a little different. Why not offer classic speed games to all non-premium members (something reasonable like 10 per day), maybe even polymorph on classic map too so that they get a taster. Most people want to play more than just classic, so will want to broaden their map knowlegde. The only option then is casual, but if you like speeders it's a bit of a pain not to buy premium.
The reason is so that new members can try out these features on one map only and if they wish to unlock the rest of the maps to otherwise premium features, they need to buy premium. When players join a site, they are looking to immediately play some games but if you offer full premium for a limited time, this will only encourage multis. People will create new accounts each time their old one becomes restricted.
UNLESS it is free trial premium that you can cancel before the end of 30 days, otherwise you will be charged the full premium. Smart sites do this.
