If I'm gonna play around in BASIC, then it's SpecBAS naturally. If I'm researching other BASICs looking for features to steal or improve upon, then yes - I'll use those other BASICs. And I have, pretty much all of them (aside from Sord M5 BASIC G, for which I can find no manual online).
BUT, if I'm gonna go do a job rather than playing around, then I'll drop into Delphi for Windows RAD development due to the pure prototyping speed or possibly C++ or Objective-C for the excellent compiler.
BASIC is for fun, not work.