It looks like they'll be about the same in terms of difficulty.
I'm working on a Marceline axe bass right now, but I had to set it aside to work on some other projects but will pick it back up this Sunday. When it's done I'll post my progress photos. It's a core of MDF, a layer of foam sheet on each side of the MDF, a layer of foamcore on top of that for an easy glossy surface. A long piece of whitewood for the neck.
I roughly followed THIS ARTICLE
, but I made the neck out of lightweight whitewood (I think the foam neck would snap too easily); and I used some carriage bolts to make attachment points for a strap. I used white bead styrofoam because I already had it lying about; in retrospect I reeally should have used the insulation foam. Bead foam is turrible.
The basic construction techniques will be the same for both Marceline's and Marshall Lee's. Since the original artwork is so simple and lacking in detail, you have plenty of leeway to customize it however you like, and still stay "canon," as it were. For instance, I'm going to try to make the scuffs and gashes realistic and believable, instead of simple cutouts as in the original artwork.
opinion: make Marshall Lee's, it'll be special and unique. Plus, it has a skull on it, and skulls are cool.