All three guys, Ivan Nova, Federico Garcia, and Philbert Hughes, want to maintain progress, and the 5th spot is likely to experience extra days between starts and skipped starts if there's a lot of rain in April. Not good to any athlete gearing himself up.
The best determinant is a weighing of practicality, the best way to win, short and long. My first thought is that Freddie should not be stressed past maybe 160, 170 innings, judging by his tiredness last year. Second thought, Freddie has some mo, having performed well throughout ST; good start, let him keep it up. In terms of mo, Phil is rolling pretty well, and Ivan has not had much command, so I would say Ivan should pitch less, and work on the side more as the 5th.
In terms of innings expectations and health risks, I need to see Verlander's, Hamels' experience in their bounceback seasons, to look for whether pressing to leather or more gradual reemergence seemed the case. Someone mentioned Greinke yesterday, must be more. Such would guide my use of Phil. Ivan, I'd be researching the other way, as in what can ease a transition to the higher plateau without causing strains.
Without all that, I'd guess on pitching Phil while he's hot, planning to rest him for a few weeks when he sputters. If Ivan shows good progress with his command this last start (Tuesday?) it's a jump ball, but if he struggles, I'd make him 5th.
When Andy's ready (if he looks great), we'll have a month of experience, to judge who is going best and who needs to work on something, either as the long man or in AAA, if it's serious. Or maybe as a setup man, if Phil or Ivan. If it last all year, doubtfully, we'll have to go conservative next year. Federico, the Chief, has been said to need longer to wind his clock; if so his use would be less flexible. If Andy doesn't look solid, or if he falters, then switch him into the bullpen.
btw, Cedeno looked the lights-out LOOGY today.