Which one I should choose for random forest?
If you are doing a classification task, use random forest classifier. If you want probabilities use predict_proba or you can use predict directly to get classes. You might be getting correct results but understand that the random forest regressor works on a different cost function, and is not constrained to give outputs between 0 and 1, so what you are getting out of the regressor are not really probabilities. If you run it on enough datasets it might start giving you outputs greater than 1. Hence, bottom line stick to classifier. Also I will recommend reading up a bit on the differences of regression and classification tasks.