What fusedpro said. I've got both a Leopold and a Filco with blues. The stabilizers and USB are the main things. The cases are a bit different as well, with the Filco being more angular. (I like it better)
Another consideration is that Leopold has slightly non-standard space bar stems which *could* make using an aftermarket set of keycaps problematic. (Basically, you'd just keep using the factory space bar, no huge deal.) But even then, sets are starting to use universal space bars that work with Leos fine.
The biggest thing is the stabilizers in my opinion. I think the Costar-style (with wires directly under the keycap on the longer keys) is preferred around here.
That said, I think the question is limiting... you should be looking into Cooler Master Quick Fire Rapid. It's basically identical to a Filco in most ways (made by the same company), but much cheaper than either the Filco or the Leo. It's not been on the market thaaat long so some of the old comparisons you have read may not include it. But I think it's a smart choice. The only complaint I have about them is the branding and keycap font. But apparently newer ones don't have branding, and the key caps are easily replaced. (I have 3 Filcos, and don't have any original keycaps in use... so that doesn't matter if you plan to buy some.)
