There have been a lot of arguments on this issue. The airplanes I've
had trouble with were usually toed-in, or had uneven alignment (one
wheel toed-out, one straight). Cessna and American Champion, among
other manufacturers, will ask for zero toe-in or out.
The RC modeler crowd seem to favor the toe-in outside wheel
scuffing drag theory, but they're operating mostly off grass and have
no idea how an airplane "feels" with toe-in or out. They spend most of
their early hours groundlooping no matter what the alignment. The RC
flying I've done just tells me that it's a lot harder than sitting in
the real thing and flying it.
The toe-in, seems to me, would be counterproductive anyway,
since the inside wheel in a groundloop has little or no weight on it,
and the outside wheel will have more say as to where the nose is going.
I'd align the wheels straight as best as I can, and tolerate a tiny bit
of toe-out, if anything.

Dan