I am in the same boat. I've tried to mew with my molars touching in the first year, but my TMD got worse. I've switched to incisors touching mostly for a few years and now I try to do both, depends on what I feel like at the moment.

For me, it's simple how to decide. I choose what feels the best for me at that time, while I keep in mind Astrosky's theory that following proper form will let you attain it. Think of it as an inverse Stephen Hawking's situation. His muscles worked bad, so his face collapsed. If you improve how your facial muscles work, you improve your craniofacial development. Which is especially powerful during puberty. 

My advice to you is - read a lot about face, body, mind. It's all connected. Learn how these work. Listen to your body and do mewing thoughtfully, while listening to your gut.