I recommend the refractor over the Mak in this case. A quality, thermally acclimated, well collimated Mak on a night of good seeing is a wonderful instrument. But that's four qualifiers...
First, the Mak needs to be of good optical quality. Thankfully, most current mass produced scopes are.
Second, it must be thermally acclimated. This is where it's easy to go wrong. Mismanaged thermals can be mistaken for poor optical quality and/or poor seeing. If you want to be able to go outside and split doubles immediately with your scope, I don't recommend the Mak unless you're storing it outside or planning ahead to acclimate it to the ambient temperature. Not good for spur of the moment observing, probably... A poorly acclimated scope yields fuzzy, warped stars at the eyepiece.
Third, the collimation needs to be dialed in. The good news is that it will probably hold for a long time. But this can be difficult if you haven't done it before. A poorly collimated scope yields fuzzy, warped stars at the eyepiece.
Fourth, the central obstruction of the Mak throws more light into the diffraction rings than with an unobstructed scope. The less concentrated image is more visible impacted when seeing is poor. A star appears as a sharp point of light in the refractor vs. a (slightly) larger target in the Mak. The difference at the eyepiece can be significant when bad seeing is making all of that light sway here and there.
A friend of mine put it well... "When all the conditions align, a (larger) Mak will pull ahead of a (smaller) refractor. But on the other 29 days of the month..." In my experience, refractors offer real advantages when the conditions aren't ideal.
I'll add: There are so many doubles to observe that one doesn't necessarily need a 4" (or larger) refractor. An 70-80mm ED could keep you busy indefinitely. My 60mm refractor is a wonderful doubles scope.
These are merely my opinions, based on my experience, and we live in a beautifully subjective reality.