It depends on the General Terms and Conditions. First, some casinos will only allow you to use your no deposit bonus on slots. In this case, slots are obviously the choice. Some casinos allow you to use your bonuses for mass and live games, although they often place higher wagering requirements on them than on slots. Read the terms to understand the different requirements and decide what suits you best. If the wagering requirement is 1x for both types of games, you probably have a better chance of winning some money if you make low-risk table bets (red or black in roulette, banker in baccarat). But if the requirements for the mainstream games are much higher, you will probably be better off playing a slot with a high hit rate.