Hi, as with many things, the style of hat will largely be down to personal preference and also the use that you'll be getting out of your hat.

I woud ALWAYS recommend that you go to a saddlery where you can have a hat/helmet fitted by a BETA qualified hat fitter, the fit of the hat and the chin strap are imperitive in protecting you if (when) you fall off! For a beginning/novice, the general recommendation is for a 'Jockey Skull Cap', the styles of these are getting better and better, both Charles Owen and Champion make some really good looking/comfortable helments, as do Gatehouse (these 3 brands, I'd say are the market leaders - and for good reason!).

Have a good look on the web to have a look at various styles, but PLEASE don't buy online as you really do need to have a helmet fitted properly.

Good luck in finding the right helmet for you!!