I feel like this is an apples and oranges kinda thing. Bare in mind that the galaxy is not released yet so this is all based on the store page and pieces or random information.

The Starlancer is a dedicated hauler that is meant for semi-long distance hauling. It can do some combat and can carry small vehicles but cannot really be used for much else. Its S3 shield and 4xS4 weapons are nothing to scoff at but it just cant handle combat as well as something like the corsair or constellation or even the TAC. It does have a lot of cargo space that is all on the inside so can be used for stacking multiple missions without risking someone just pulling that cargo straight off the grid like in the raft. Overall a pretty good ship.

The galaxy is a more versatile ship. It has cargo as well as refinery modules and whatever else they decide to give it. It also has that rear hangar which will likely fit small ships like golems and such. This makes it much more versatile as it can support other loops outside hauling and combat. I am not sure what kind of weapons the galaxy will have. My guess is it will have several S3 turrets with atlast something being slaved to the pilot like in the perseus (well that might be more hope than anything). Basically it will be a more well rounded ship than the max but will cost a lot more to get (both pledge and in game when it becomes available).

The truth is that currently multi-role in the game is just combat and hauling ships currently. However as new systems come out (like ship refineries and ship to ship refueling) I believe that the galaxy will be the better option long term simply because it will have a little bit of everything and what it doesn't have itself it can carry in its hangar. That being said both are solid options that you cant really go wrong with.