I open the cap and then pop the lower hose off. Use a 12 gallon plastic tote to catch the coolant... I usually only lose about half a cup or so, then hose the area down.
Removing the radiator cap first allows the coolant to flow steadily instead of going everywhere as it repeatedly pulls a vacuum, sucks air back in, splashes coolant back out, etc.
Honestly it's that blasted quick disconnect fitting on the lower side of the tranny cooler that pisses me off the most :smsoap: I usually chop it off and replace with a pair of fuel injection clamps, one before the ridge the other after, it takes a dip in some boiling water to get the hose pliable enough to go past the ridge and after that it's not going anywhere.