If you don’t mind playing just a single mobile video slot predetermined by the casino, then by all means pick a no deposit free spin bonus. They are usually linked to specific popular or new slots by the casino. But if you want some freedom to pick your slots with a no deposit mobile bonus, you have to claim a no deposit cash bonus.
In almost all other aspects, free spins and free cash/credit bonuses are similar. If the considerations listed above don’t really matter to you, base your choice on the relative size of the no deposit mobile bonus – ie, how much free cash do you get from the offer.