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For pistol (straight wall) brass, you will see most IDPA and USPSA shooters using mixed brass (other than maybe a handful that are trying make major power factor in a caliber that was not intended for that in USPSA). Like others said, if you are going to load hot, you should stick with the same brand of brass.

I use mixed 223 brass for our AR carbine matches. I load to 223 levels and have had no issues. I use bulk components (powder, primers, bullets) to save costs and still get very acceptable accuracy results. When I load to 5.56 levels, I only use the same brand of brass and only brass that has a head stamp for 5.56. I resize the 223/5.56 brass then trim to minimum case length.

For long range precision shooting, I use the same brand and am moving to Lapua brass (for precision shooting) as it produces better results and the primer pocket does not open up as quickly.