It depends entirely on what you and your horse find easier
N27 is all about self carriage - 1/2 10m circles, give and re-take in canter, transition to trot off a diagonal of canter
N28 is a bit more about suppleness and balance - serpentines, 1/2 15m back to the track, beginnings of counter canter
My advice, ride them through at home and see which you find easier.
Hope that helps although doesn't answer your question directly.
I think n28 catches most people out not with counter canter but the downward transition through that corner after is very tight and most look extremely unbalanced through it and you have to do it on each rein so personally think 27 runs smoother if a choice of the two x