I very much prefer good concrete tees, but I'm happy playing from anything that's level and not slick. Unfortunately, that usually means I'm not happy playing from rubber tees. Other surfaces like astro turf and carpet that I've played off are perfectly fine if installed well, like the tees at Richmond Hill. Even natural tees are fine by me as long as they aren't rutted or full of roots sticking up.
I've heard bad things about rubber tees a lot. Personally, I found the tees at Shawnee State Park to have excellent grip. And I've played early in the morning with dew and the ground and during a soft rain. I thought that they were fine even when wet. I found that early morning dew made the nice concrete tees at Buchmiller Park more slippery than the rubber tees. That's just my personal experience. And I agree with you that any level tee is basically OK in my book.
This is what I love about DGCR. Getting all of the different ideas is great. I continue to learn something new almost every time that I'm on here.