First off, I would not use pellets. If I had an Omega and was going to shoot pellets, they would be Pyrodex Pellets because those are what Thompson Center recommends. There are advantages to all kinds of powder and disadvantages....

Triple Se7en powder is know to produce a hard crud ring at times in Omegas. It is necessary to swab the barrel sometimes between each shot. Some posters claim they have to wire brush the barrel between shots. You get a good clean burn with Triple Se7en which leaves very little fowling. Yet crud rings can be made less with a softer ignition.

Pyrodex Pellets are the old stand by. They work great. You still have to swab the barrel. Usually the fowling is soft and will swab right out of the barrel. Pyrodex leaves more fowling in the barrel and takes longer to clean the rifle some say after you're done shooting at the range. They are recommended by the factory reps.

American Pioneer Powder Sticks leave the least of all in the fowling department. Some people are not comfortable with the way the sticks are made because of the lack of uniformity they find in them. Chunks are missing off some of the sticks. When you're looking to stay consistent for accuracy you do not want large differences in anything I guess. APP is also said to be very moisture sensitive.

Pinnacle also came out with pre measured I was told but have never seen them or read of any posts where they were used.

I am not sure if Black Mag3 has pellets, but in FFFg loose form many Omega shooters are getting some good results with it. Loose powder is not really harder to use then pellets. You can pre measure out the loose powder into speed loaders for hunting purposes and load as fast as you can with pellets... I guess the choice is up to you.