Depends on the rifle, really.
Mary Beth seems to really enjoy either Federal Blue-Box bulk-pack, or, oddly enough, Red-box bulk pack ammo the most. Mind you, I haven't fired any Eley or anything through her yet, but it's on the to-do list. The best groups so far were, strangely enough, shot with the much-maligned Federal Red-box bulk pack ammo. Which probably a 98% reliablilty rate with this particular rifle, the other 2% comprised mostly of rounds that got jammed due to last-round-in-the-tubeitus, which has happened with pretty much every different round I've tried so far, so I won't hold that against it. They've all gone bang on the first hit with this rifle.
The M-69, on the other hand, likes CCI Mini-Mags the best. It, however, is not always a guaranteed bang every time, either, with both CCI, Federal, Remington, and Winchester .22's having failures to fire due to what seems to be light primer strikes. That being said, the CCI's shoot noticeably better, when they do fire.
