When carrying two spares and I'm not wearing my radio, I like the Raven double Copia.
When carrying a single spare (most common off-duty and admin), I like the Raven single Copia.
When carrying two spares along with my full complement of gear, I find the Blue Force Gear 10-Speed to be a good option....it's overwhelmingly popular at my work. If you're using Glock 19 15 round mags, the draw speed sucks and is fumble prone. If you're using Glock 17 mags, or 19 Mags with an extension (I'm using Taran Tactical +5s), then it's fine. Concealment isn't as good as the Raven pouches, either.
With my prior service weapon, the SIG P229, I used single Basic Mag Carriers from CCC. They concealed great, and being narrow singles it was very easy to arrange them in a good fashion around the other gear on my belt.
When I went through a more demanding 3 month training course that featured a lot more pressure testing in adverse conditions than the basic agent course, I found out that the level of retention from CCC BMCs and the like (Kytexs, and some other brands I can't remember that I was issued), was not acceptable. I constantly lost mags. So, I tightened down the Copias which gives me really good retention, and also negates the issue with the retention screw falling out as I found to be an issue when setting them to CCC BMC/Kytex levels of retention. The BFG 10-speed also has good retention with Glock mags, much more so than the BMC or Kytex.
YMMV.