I recently took a few defensive shotgun classes, which I'll review later.
I'll keep this one short and sweet:
The Federal Tactical Low recoil 00 buck had a very tight pattern:
Out of a stock 18.5 inch cylinder bore Mossberg 500 barrel it did
2 inches at 5 yards
3.25 inches at 15 yards
6.5 inches at 25 yards
It also functioned flawlessly. I bought it on http://www.ammunitiontogo.com/.
The Rio Royal low recoil 00 buck had a very wide pattern (I didn't measure it, but at 7 yards the pellets would be all over a human torso). It also did not feed very well into my Mossberg 500's mag tube. About one out of every four rounds, the shell would stick a little bit as I was trying to shove it in, and I would have to wiggle it around a little to get it to go in. It was usually sticking around where the brass entered the mag tube. Feeding from the mag tube to the chamber, and extraction and ejection from the chamber was flawless.
The feeding issue with the Rio Royal was a big problem to me, I don't necessarily mind a wide pattern for training, but difficulty loading the gun is a deal breaker. While it was significantly cheaper than other brands, I would not buy Rio Royal ammo again. I think I bought it from http://www.cabelas.com.
Regarding feeding, Rio Royal is high brass while the Federal is low brass, but I don't think that was the problem. I have tried some Remington ammo that was high brass and it fed into the mag tube without problems. I think the Rio Royal brass was just slightly out of spec in its dimensions.
As an aside I should mention I also fired a bunch of Winchester Super-X birdshot, Winchester Super-X slugs, and Federal low recoil slugs. All functioned perfectly.