I was told i have a tumor on my left temperel lobe and now my doctor says he thinks its a cyst. which is worse?

Cysts are benign: A majority of the cysts are, by definition, benign. So , if it is indeed true, then you are going to do better with a cyst. So a tumor is typicall much worse than a cyst. But we have to make sure(with longer follow up) that there is no growth in this lesion, as tumors can sometimes look like a cyst and be misleading. Only longer follow up monitoring would help to make this distinction more certain.