I've probably assisted with more rescue classes than the number of dive classes I've taken. I suggest you take the class where you will do most of your diving, or in similar conditions, so you get the best taining and feel for realistic conditions and scenarios you'll encounter in your diving. Then find the best instructor you can for the area.
The rescue class is like drinking from a fire hose. If you can master and retain 20% of what is covered in the class you're doing good. A year later if you really remember anything and can perform you're exceptional. Unlike most skills taught in dive classes, hopefully you'll never need or practice what you learn in the rescue class. The best thing to do is after your rescue class to keep coming back and helping by playing victim for future rescue classes. You will be amazed at how much more you learn that way than you actually did in the class, and it will keep you relatively current on the knowledge from the class