It may be appropriate to compare products from manufacturers of all three.  
http://www.alliedtube.com/html/ecd.htm
http://www.westerntube.com/conduit.htm
http://www.republic-conduit.com/flash/
  

The I in IMC is intermediate, not rigid but not EMT.  It uses fittings like rigid conduit but has reduced wall thickness.  Personally I think it works well for most industrial environments, the exception being extremely harsh chemical environments where even rigid should have a PVC jacket.

At most industrial (and even commercial) installations I've seen, IMC is generally not used.  They either select EMT for light duty, or RGS (rigid galvanized steel) for heavy duty.  The philosophy being that if the environment is abusive enough to warrent IMC or RGS, they might as well put in RGS, given the relatively low difference in cost of IMC and RGS.  RGS will withstand a blow from the proverbial fork-truck much better than IMC.

So far as I know, NEC treats IMC and RGS essentially interchangeably, whereever one is permitted, the other is OK too.  I'm pretty sure that even applies to hazardous explosive installations (although you might wanna double check that).  

So all in all, it really comes down to your environment, your personal preference, and your budget.

Beware, lots of IMC is aluminum -- obviously, if you're in concrete, you don't want any aluminum.

A frustration can be that some IMC requires installation tooling that is slightly modified/optimized/adjusted compared to that for GRC.
  

By the way, at the other extreme, I know of at least one manufacturing site that runs all their 5kV lines through EMT, unless they absolutely positively have to put in something more substantial.

I have run all three and prefer the IMC because of the strength and ease of bending compared to rigid.  It also tends to have a better surface finish than rigid.

Barry

Barry,
   I have had the opposite experience with IMC, but it was a number of years ago.  It seems harder to bend than rigid because the steel itself is harder, and we had trouble with the  conduit breaking at the threads in the sizes under 1".  The wall thickness of IMC is less than rigid and when you thread it  there is not much strength left at the threads.
Don