The bigger tire will give you slightly higher gearing due to the higher diameter. You should get a trainer specific tire, as the compounds are harder to prevent overheating/excessive tire wear. Your tire isn't slipping against the roller on the trainer in either case, so the power transfer argument is relatively moot (theres rolling resistance and what not, but its not something you should be worrying about on a trainer...).
The reason why you'd get a 700x25 tire over a 700x23 tire would be that if your rim was wider, it may support a 700x25 tire better. This is why some trainer tires are produced in 700x23 and 700x32 (e.g. Continental Hometrainer-- the larger size will fit some 29ers barely, which have wider rims). Most road racing bikes are designed for 23's so its easiest to ship 23's, which most trainer tires are, for road bikes. Also, there exist frames which will rub with a 25 but not a 23.
The TL;DR version: pick whichever one you want, provided your frame doesn't rub.
Also, I didn't find anyone actually producing a trainer tire for 700x25 -- there are training tires for 700x25 but they're for the road, not for the trainer.