In regards to which is better to have performed, the drain & refill or a complete system flush, provided either are actually an option for these cars...my understanding (and take that for what it's worth) is that it's generally best/preferred to perform a full system flush if/when you are doing so at regularly scheduled intervals. Essentially, the school of thought being that if no service, or irregular service, had been performed and the vehicle is "high mileage" there could be "gunk" in the system that is "holding things together" that if flushed out could reveal/produce other problems. For example, bad seals could be more likely or prone to leak after a full system flush. Whether you believe or agree with that or not is up to you but an interesting theory nonetheless. Again, that would typically only apply to a "high mileage" vehicle that had not been previously or properly maintained; in which case you may arguably want/expect to see other problems anyway. Food-for-thought :-)
'08 Lexus IS F (Ultrasonic Blue Mica) | '02 Harley Davidson Edition F-150 (DSG) | '13 Suzuki Hayabusa (Pearl Glacier White)