I like Osmocote. I had to buy some Shultz brand when I ran out re-potting mums:
https://www.menards.com/main/outdoor...56040199610166
The Schultz mums did ok. I have not tested it on other plants yet. It did make one pan of water go dead-animal stinky, but that only happened once. It's still probably not the best choice for a sub-irrigated planter.