Back in the 80's and 90's Audio Research and Conrad Johnson

We're very competitive with each other. It seems like the main dealers at that time had one or the other. Nowadays you rarely ever see Conrad Johnson at a Brick and Mortar. ARC on the other hand is more popular than ever. Do you think this was mostly to do with marketing or Did ARC just come out with much better products than CJ?

Being an avid Conrad Johnson fan, my take is that CJ takes slow, steady, measured steps. Their gear, especially the higher end is stunning now. Probably not much to improve.

ARC keeps updating and improving, coming out with new models and keeping their name in the limelight.

ARC and CJ have slightly different flavors. My feeling is CJ is a touch warmer, ARC a touch cooler. Both superb but appealing to different tastes. 
ARC always=more accurate/resolving  CJ=more coloration/warmth  Absolutely a matter of taste.   The public expressed their tastes/opinions and the newer CJ gear moved toward resolution/less coloration    Strickly speaking tubed here.     No experience/observations regarding SS, in either case. AND(of course)- that's just the way I've always viewed the senario
I liked ARC (tube gear) more back then and have been using both for a while. CJ SS amps were great but not superb, except for e.g. the MF80 (a bit too warm but for those days great), MF2250A and esp the MF2500A. Never had the Premier 350 that has (still) quite a following.

Some how I leaned towards CJ in the 90s as I had a great relationship with their tech department as I modded every unit (Remember Ed, Joe?) from the PV3 to the PV12.

CJ’s modern tube amps have a.o. their proprietary Teflon caps which are leaner and provided more details, with the proper (NOS) tubes, it "Just sounds right"! My LP140m sound completely different than, e.g. the Premier 11A that I had.

I wonder what the future have in store for these companies..
Having owned several of each during the "golden age" of the 80's and 90's and listening to virtually all of them during that time when they WERE both widely available at B&Ms, I agree that the CJ's were generally warmer. Another notable difference between the two is that ARC products had a more immediate, upfront presentation and the CJs more laid back or midhall. I don't know if that STILL holds true as I haven't had the opportunity to listen to the later offerings of CJ but I can imagine that I could own an ART (90's) or GATT (current) and never look back: REAL improvements in a well designed piece of audio gear can be gotten by modification of current parts which can improve performance dramatically as I have recently discovered in a PV9a from that era which I am totally enjoying.

My impression of some of the later ARC gear is a focus towards  greater "accuracy" and "neutrality" through more  modest upgrades to keep the loyal fans coming back, marketing.  It seems CJ has taken a different approach offering fewer products at longer intervals for what reasons I know not. They certainly were more prolific during the 80's than ARC when you add in their Motiff and Evolution products! The Motiff from that era was the ONLY ss I would have considered owning. Throughout the 90's until now their offerings were fewer and farther between after the ART was introduced in the mid 90s. Their current GATT is the same price. Whether there are notable improvements between those 2 products I sure can't comment on as I've only heard in unfamiliar systems.

I have found the build quality of both products to be superb and don't believe that is the issue. The proliferation of so much tube gear over the past 25 years when in the 80's there were only ARC, CJ, CAT and VTL and a few other more minor brands along with the overall decline of the number of Brick and mortar shops seems to have had more an effect on CJ. It seems ARC has done a better job over the years marketing and  as a result their products are more readily available but I sure doubt  in any meaningful way "better" than CJ.
I'm not 100% sure, but I believe that ARC was acquired by a private equity firm some years ago.  Consequently, ARC may have more financial wherewithal to maintain/improve their market presence than does CJ.

As to their relative sonic merits, I've owned several pieces from ARC and generally liked the sound.  I have only auditioned CJ (long ago) and agree withe consensus here that it seemed a touch warmer.  However, I'm not at all sure that that delta equates to their relative market position today.
They are currently owned by Fine Sounds of Italy. Which also owns Mcintosh.
Both are still great companies making excellent products.
I like the fact that each companies' tubed pre-amp can be mated to a solid -state power amp to excellent results.

CJ recently moved to a different space in Fairfax VA, anyone know why ?

Keep me posted & Happy Listening!
i sold and delivered one of the first pairs of Prem 2 and 3 back in the day. They were VERY involving and the depth of image far exceeded ARC gear it replaced. I eventually owned a 3 and MV45-A with Quad ESL that was incredible sounding. I think CJ never had the dealer base that ARC did , they never embraced a balanced architecture, late to digital and DACs ( although the DAC they offered VERY musical. and the product aesthetic is a real hodgepoge...
IF I open a B and M shop CJ would be on my shortlist..IF it were not available at a discount on Amazon....

"CJ recently moved to a different space in Fairfax VA, anyone know why ?"

Smaller space.  Appears to be a budget cut.
ARC was more popular around 1990, and had twice the number of employees that it does now. Their old plant in Minnetonka, MN was also bigger than the current one. They sell fewer, but more expensive, products now.
Even though ARC sold a lot more of their gear 25 years ago. I wonder if there sales volume in dollars is close to the same? 
Tomic601, that "involvement" you speak of is how I remembered CJ back in the day and what I am now hearing now with the upgraded PV9a with a DRAMATIC improvement in the line stage over stock. The placement, spacing, images and tone just sounds so natural on ALL music!  I sure have heard more accurate since there is that added warmth with the CJ but I just don't care, it really   "just sounds right".  It's got me curious about their current offerings.