All good points and suggestions raised above. Very good question, whose scope can extend beyond taxi phraseology, to all sorts of possible clearance ambiguities.
I'm somewhat fortunate in working at an airport with one runway, a parallel main taxiway, and 9 connecting stubs;no high speeds. Have thought about this a bit in the past and come up with "first possible left" (or right) or if no pressure, "any taxiway", and where it matters due to busy taxi situation, specifying the route in advance, using numbers/letters. Especially so when itinerants or non-english speakers visit.
Where it's going to be tight I ask the pilot to expedite clearing, but generally only when the aircraft is still at least 1nm final..give them a bit of time to set it up. I figure if I'm too busy to plan that far ahead and warn someone in advance of any unusual requirement, maybe I'm trying to play it a bit tight.
All that said, hopefully it will be fairly obvious to aircrew that in busy times minimum runway occupancy is important.
Definitely avoid the phrase "next".