I did this one way back when the first forum started and it was a lot of fun.  For me, it was my 1983 Yamaha XJ900RK, or Seca 900.  Had her for ten years, and two weeks after I sold her in 1999 a friend brought me a copy of Motorcyclist that listed it as number three of their top ten of all time to hold on to.  I would buy another one in a second if I had the chance.

I've owned several...GL500i, Voyager12, C10.   They were good while I had them but I'm glad I've moved on.

1976 Honda MT250

It would without a doubt be my beautiful 1983 Honda V45 Interceptor! I have regretted selling that bike since the say I sold her to move back north in 1985. People have suggested picking up a old used one and restoring her (like I'm doing with my 86 C10). But I don't do it because then it won't be that cutting edge sport bike I loved back then. Now it would be an restored antique. It may still be a great bike. But I've been afraid that I might now be disappointed by the old girls performance. And I wouldn't want it to ruin my memories! 

Yamaha XT500 

Paid around $500 in 1978, sold it in 1980 for the same price. Now OTP they're much sought after and now going for upwards of $3000 

 I like full on sportbikes and have owned a few .
My 03 gsxr 1000 was the best in every way . I just really bonded with that bike.
I put it on the racetrack for a couple of years and boy did it shine.
.I miss that bike and kick myself for thinking there was better out there.
Out of 20+ bikes thoughout the years its the only one I regretted  trading off.

My SV 650 naked "spyderpig"
I never should have sold it to my son.  Still it sits and rots.

1979 BMW R100RS Blue and Silver, best fairing I've ever ridden behind. Very nice bike, very little power but it was a blast to ride and oh so easy to wrench on. I've wished I still had it thousands of times.

83 CB 1100F

1967 CL160....bought it in 1974 ...advance plate weights had rusted and were sticking so it didn't run worth crap.....fixed that and away I went.

1971 Norton Commando Fastback.....guy had put some serious coin into it with alloy wheels and proper parts then needed cash when things went bad for him....bought it, lived with it, loved it....and flipped it to make some money.

This is depressing for a Monday morning.....

Suzuki TrailHopper, would love to have had it for my kids!!!

Almost all of them.

60's era Suzuki 50 (road version)
60's era Suzuki 90
60's era Honda 180 twin
60's era Honda 250 Dream
Suzuki T500
KZ1000 MKII or IV (can't remember) - probably the sharpest looking bike I've ever had.

Other 'also had's' that I just never really bonded to, even though they were nice bikes:

77 Yammie XS750
80 Honda CB750K
99 Kaw Voyager XII

Still Have:

2000 Kawasaki C10 - the do everything go anywhere work horse
1995 Kawasaki GPZ1100e - great sporting and touring bike for me - just not enough wind protection for touring most parts of the year (live in MI)
1982 Suzuki GS1100E - if I have to explain, you wouldn't understand
1974 Yamaha DT175
1979 Honda XR250

I should not have sold any of them!!!!

                   My mint condition 1982 GPz 1100 which I bought new and kept for 23 years.  However, it enabled me to buy my 2006 C10 which I really enjoy.

I can't say that I "shouldn't" have sold any of them, as it seemed like the thing to do at the time.  I still occasionally miss my:

82 CBX
84 Nighthawk S
77 CB400F
79 CB750K
74 CB450
06 SV650

I loved them all, and still have the great (and a few not-so-great) memories.  Probably miss the CBX the most.  That engine had a lovely, soul-stirring sound.

I might get some flaming for this, but I really miss this bike.  My 98 Buell S1 Lightning.  It was the cool blue and orange.  I put a lot of extras on it.  Yeah, I had some issues with it, but that bike had a lot of character and I even made it from DC to Asheville, NC on the BRP. 

I did this one way back when the first forum started and it was a lot of fun.  For me, it was my 1983 Yamaha XJ900RK, or Seca 900.  Had her for ten years, and two weeks after I sold her in 1999 a friend brought me a copy of Motorcyclist that listed it as number three of their top ten of all time to hold on to.  I would buy another one in a second if I had the chance.

I have on that needs a lot of work with clear title that you can have if you want it.  It's a 82.  I just don't really want to mess with it.

To answer the original question, I should have never sold my 88 hawkgt - I had gathered up the cbr f3 front end, the VFR back wheel, and had polished the frame and swingarm.  I had a spec II fairing for it as well.  Mike Velasco had agreed to rebuild my engine for 75 hp on premium gas.  But I decided to go another way and sold it cheap.  Dumb, dumb, dumb.

I also wish I hadn't sold my 84 V65 Sabre.  That bike was a hoss.  Hondaline fairing, KZ1000 hard bags.  Basically a concours.  I had well over 100k on it.  The guy I sold it to (as a favor to help him out) blew the engine 2 weeks later and scrapped it.

My '05 Suzuki Bandit. A Swiss Army bike if there ever was one. Plus the '05 is the only year they came out in blue & white gsxr paint scheme, also the last year for the oil/air cooled engine. Oh for the simplicity of that motor. I hope when I finally pull the flies on my connie that it gives me the same low-end torque rush the Bandit had.

1986 VFR750 Honda in red/white/blue. The GOOD one with the sandcast engine covers. Sold it for more than I paid for it 10 years earlier and knew it was a mistake the instant I saw anyone except me on the seat!

dumbdumbdumbdumbdumb . . . .