Rob... it obviously depends on what your needs are, and what you're shooting. For 4x5 I have been using a Toyo AII since 1998 which has served me well, with all of the movements I have ever required. It even got me through 2 years at Brooks Institute, where I only needed to rent a monorail once because the Toyo couldn't be turned into a pretzal for a truly tough assignment. I also just picked up a Carbon Infinity, which has movement capability out the yinyang, partly from curiousity and partly because I'm starting to shoot more architecture.
That being said, I have probably shot more 4x5 film in the last 10 months with the 45PS than I had in 9 years with the Toyo. It's so light, so quick, and so easy that I take it out far more often... simple as that. Obviously there are considerations you have to take into account... lean more towards WA lenses, change your position if perspective is an issue, use smaller apertures, etc., but in the end nothing beats a bigger piece of film. Every great shot ever taken with a Hassy, Fuji 6x9 or Mamiya 7 would have been even better had it been captured on a bigger film. Fortunately for us, quite a few other folks feel similarly.