EZDrummer is the only software that Ive used and been asked "is that a live kit."  To me this was devastating as I only want my live drums to sound live, so I quickly retracked the drums afterwards.  But maybe this is what you are looking for.  On a different note, in my opinion; EZDrummer hits my CPU much harder than Addictive Drums.
 
This is one mans story, other experiences may vary.... 

Yes........Demo them all & buy them all.

Of the drum synths I've used, EZD, Session Drummer, Addictive Drums, EZD is by far the easiest and most intuitive.  If I had the big bucks, perhaps I would have gone for Superior Drummer, but I'm totally satisfied with EZD.
 
Btw, I am one of those the singer-songwriter types, country/americana/folk.

It seems I'm against the grain a bit here: bought/tried them all and use Addictive Drums2 all the time. They sound the most realistic to me. I occasionally use EZD's Reggae and percussions kits but not their others.
It depends on personal preferences and genres I guess, so trying demos is the best route.

If you are looking for good drum sounds and simplicity in writing parts for songs
you cannot beat EZDrummer 2.  It will actually do a LOT of the work for you, and 
the EZX's are decent.  If you're looking for "real" drum sounds that you have to 
tweak and do the actual Engineering on, then BFD 3, Superior Drummer, and
the 2 East West Pro Drummer Libraries are pretty "on par" with each other, but
I give BFD 3 the nod for being the best.  The samples are raw and detailed, but
it's only a slightly better then SD.  But SD is a quicker in getting good results.

If I had to pick ONE, it would be BFD 3...

I use EZDrummer to write my parts, then replace it with the Program I feel 
best suits what I'm doing...

Skyline_UK
It seems I'm against the grain a bit here: bought/tried them all and use Addictive Drums2 all the time. They sound the most realistic to me. I occasionally use EZD's Reggae and percussions kits but not their others.
It depends on personal preferences and genres I guess, so trying demos is the best route.

Same here...   Every one of my projects uses AD2 for acoustic drums.  For electronic/other percussion I like to use or layer Battery 4. 
 

Superior Drummer is usually the one that gets into the final mix on all of my tracks!  Just sounds great and realistic.

Mesh
Yes........Demo them all & buy them all.

AS a graduate of the FSOSA, you would be expected to say that. And, of course, you are right. According to the rumor I stared with myself, when Superior Drummer3 gets here with the EZD2 features that will be the biznes. I am in saving up for it mode, though there has been no word about it. It will have been 2 years in March since EZD2 was announced and 2 years in May since release. They seem to have a big deal in May and November Metal Month. Last May was all the wonderful Muscle Shoals related stuff. I am hoping for SD3 this May.

BFD3 if you want a superior experience.

EZD2 (and a lot of EZX expansions) does it for me.  I actually own Superior Drummer2 (as well as AD) but I like the relative simplicity of EZD2, and since the version 2 upgrade, it has all the basic tweakability I need. 
 
You can start with EZD2 and some expansions, and see if that suits you.  If you want more tweakability, you can upgrade to SD2.  The beauty is, it'll play all of your EZD expansions just fine.