You didn't state what the source of the endo gas was going to be but if you plan to generate it here is some thoughts.
My experience has been the N2-MeOH is the better of the two if you your have a low volume of work and intermittent operations. We switched from one to the other for several years depending on the work load of the furnaces. A point missed by some people is that if an Endo Gas generator is used it requires more attention and an experienced operator.
You will have to look at the economics between the two depending on the source of N2, the cost of heating the generator, the volume of gas needed, and maintenance costs, etc. As our generator aged and along with a intermittent operation the maintenance cost went up. We eventually went to all N2-MeOH due to concerns of non-odorized gas in the shop. The odorized gas requirements eventually caused the furnaces to be moved due to the necessity of having a flame curtain when opening the boxes.
There has been a large amount of work in this area, much of which was published in the "Heat Treating" magazine. There has been quite a lot of improvements in both systems so I would recommend a good look at all systems.
