Of course RSC is the safest, you can be sure the watch internals are serviced and original when you get back the watches, but this is the most expensive route. I'm also gonna service both my watches soon, but the thought of spending all that cash is the main reason why I'm procrastinating.
The other is to take them to a trusted 2nd hand watch dealer for their indouse servicing, I've heard some of them have hired former Rolex technicians for the servicing.....not sure about this though, or whether to trust such shops. The benefit is of course lower servicing costs....