Douglas - I would recommend Kadees. They are the standard "aftermarket" coupler for a reason. Tough, work well, and come in different configurations for almost every application. The "scale size" #58 are nice, but the standard #5 are great as well.
ADDITIONAL info - about your first question. Most of the magnets are in a specific location, and are always "on" (only electromagnetics can be turned off and on). You park the connection you want to uncouple over the magnet, and after a little back and forth to introduce slack in the couplers, they come apart due to the magnetic force. Theoretically, if you do not have slack in the couplers, they do not uncouple. However - read on...
Gary - I would not recommend the uncoupler magnets for any area you can reach with your hand. Get an uncoupling "pick" instead (bamboo skewer, small screwdriver, specialty Micro-mark tool, etc, etc). If you do want to use them, use the electromagnetic ones that can be turned off when you don't want uncoupling.
We used the standard "between the tracks" type one one of the local club's modular display. The module is for use at shows and meets. After much debate, we decided to remove the magnets because:
- they uncouple when you don't expect it - any slack in the train can lead to unwanted uncouling
- they are only located at specific spots, but you may want to uncouple elsewhere
- they don't uncouple when you DO want it if you aren't super smooth on the throttle, and aren't using a well running engine with excellent slow speed capability
Besides, the prototype does it by hand, and if it's good enough for them...
Andrew