I'm thinking of building up a 9mm so I can shoot it at work.  However I can't decide which way to go.  I like the idea with the oly's that you can use sten mags and don't have to use a special hammer, but I like the fact that the colt/rra have more mag block options out there and that TROS has a 5" barrel for them.

What would y'all reccomend

1st, If I may ask.  What is work?  Military/Security/LE duty use?  I only have OLY 9mm AR's.  I would never use them for duty use.  Colt all the way and RRA in second.  My OLY runs like a champ and has never had any problems.  If its duty you have to deal with storing those OLY modified mags(welded on blocks).  Colt just pop them in a regular mag pouch.  Just my 2 cents.

colt 6450
colt mags
6k rds without a single failure.

i work at an indoor gun range/gun shop and I wouldn't use the welded mags.  I'd probably go with the SNS mag blocks.  

But I like the fact that the Hahn mag blocks have feed ramps for the colt/rra

Well OLY is a great plinker as is Colt and RRA.  I have an OLY GL9 flat top that uses factory Glock 18 33 rounders.  Its ready to shoot right out of the box.  No need to switch hammers etc..  But it is a dedicated lower.  Which is a plus because its solid and one piece, thus no worries about mag block problems.  Most will say they dont have any mag block problems but AR15.com is full of people chatting about their mag block problems.  But with a mag block model you can pull it out and use for 223 if ya wanted.  I still like the COLT's.  But I made my decision and I'm happy with the OLY.

Quoted: i work at an indoor gun range/gun shop and I wouldn't use the welded mags.  I'd probably go with the SNS mag blocks.   But I like the fact that the Hahn mag blocks have feed ramps for the colt/rra

which indoor range do you work at?

champion firearms in college station

Quoted: Well OLY is a great plinker as is Colt and RRA.  I have an OLY GL9 flat top that uses factory Glock 18 33 rounders.  Its ready to shoot right out of the box.  No need to switch hammers etc..  But it is a dedicated lower.  Which is a plus because its solid and one piece, thus no worries about mag block problems.  Most will say they dont have any mag block problems but AR15.com is full of people chatting about their mag block problems.  But with a mag block model you can pull it out and use for 223 if ya wanted.  I still like the COLT's.  But I made my decision and I'm happy with the OLY.

+1

Just make sure you use Glock mags and not aftermarket.