I have an 9mm AR15, and an HK94 clone.

After the "9mm carbines suck" thread, I've been thinking about selling the 9mm AR upper and building a 5.56 one.  My thoughts are that:

1) they do the same thing (except the AR won't eat cheap ammo w/o the can),
2) both have expensive ass mags, so I'd rather focus on one, mag wise,
3) the 9mm setup in an AR seems like an after-thought, which I guess it is, and mine has an insatiable hunger for $10 bolt catches despite the $2.00 shoved in the buffer tube,
4) I don't have a shorty in 5.56

Other option is wait a while to buy the 5.56 upper, and slap the 9mm setup on the pistol lower that I have collecting dust.  I suppose then I could decide which is best.

Is there any reason you can think of to keep the 9mm AR setup over the HK-clone?

The only thing I am coming up with is range availablity. Around here indoor ranges are easier to access and are generally restricted to pistol cals. If you want to train with an AR type weapon but have better or easier access to a indoor range then the 9mm comes in handy.

Personally, I prefer the MP5 to a 9mm M16 so I'd ditch the 9mm upper and go .223 on the AR.

I like the HK better also. I think 9mm AR's look pretty cool...but they aren't really that practical.