Utah in October or November...or April?

I have been to Moab in late April 10 times and once in late September. Got rain one day out of a week in the September trip but in April I have seen snow, rain, heat, and all "perfect" during a weeks visit. More "perfect" weeks that ones with bad weather. I feel that late April/May is a better time than September/October because in the spring the weather should be getting better where in the fall it will be getting worse. But it's unpredictable...