You should follow the school's instructions - some schools specifically ask you to provide a recommendation from your current supervisor, or to explain if you can't.

Hi... if you feel that previous supervisor can do better justice in bringing out your qualities, then in my opinion he/she should be writing your reco... the main purpose of recommendation is to verify your contribution at your workplace. Best recos are those where the person giving the recommendation has directly worked with you and his/her work performance was in some capacity linked to your performance.. however as correctly answered above, recency of relationship is definitely advantageous but not a mandatory issue with the recommendation. Content of the reco matters more. I hope it helps.