On my 1911s, it really doesn't seem to make a difference, so as long as there's balance between the MSH and trigger length; my SIG GSR XO has a flat MSH and a longer trigger, where the Colt Series 70 Repro has an arched MSH and short trigger. For me, it seems that the critical factor is finger placement on the trigger, and which combination achieves that best. Other factors can be frame and grip variations.
Best, Jon