Horse races basically take two forms. They are either run on the flat or over jumps (commonly called hurdles). There are advantages and disadvantages of betting on each type.
With jumps, there is a risk that the jockey will fall off the horse. It is sometimes possible for them to get up and continue but even if they do it is unlikely that they will make up the ground they missed when falling. However, it can be much more fun, if you are not sure whether the horse you have bet on will even finish the race. However, if you want to have a better idea as to whether your horse has a chance of winning then maybe choosing a race on the flat will be more sensible as there are less likely to be horses that do not finish, although it can happen.
If you like to bet on a horse with the type of odds that could win you a lot of money then it is probably better to do so in a hurdles race. The horse probably has a better chance of winning because it is possible that some of the good horses may ditch their riders on the jumps and therefore not finish. IN a flat race it is more likely that all the horses will finish.
Some people just find one type of racing more entertaining than the other and this will effect what type of race they prefer to bet on. Others do not really mind which. If you are new to horse racing then it is a good idea to watch the different types of race and then you can decide which you think you would rather bet on. Both can be great fun and exciting and you may even decide that you like both.