With the exception of Gloogas, all Dualies are viable. Both variations of Dapples seem to be the most used right now.
Splat Dualies - My personal favorite, even if it's considered the second worst. They have the Burst Bombs for nice aggressive play. It's just that most people don't see the point of them because the Splattershot does the same thing, and "better" special. I'm working on a way to embrace the Tenta Missiles, and use 'em aggressively with the Dualies and Burst Bombs. I'll show those jerkfaces to call Splat Dualies bad simply because they have Tenta Missiles.
Enperry Splat Dualies - One of the more popular Dualies. Afterall, this has a niche over the .52 Deco and Sploosh by being able to dodge roll out of your Curling Bomb trail. It'll make you less predictable and more difficult to hit, since everyone is wary of the Curling Bomb follow. Of course with the Enperries, you'll have to learn to get used to Inkjet in a way that doesn't get you killed. If you learn how to use Inkjet and some cool tricks with Curling Bombs, I can see someone being deadly with the Enperries.
Dapple Dualies - Probably the most popular Dualies, and what most people consider the best weapon with Beacons. Afterall, it has great mobility and is deadly at close range. The Suction Bomb launcher also make it good at turfing/pressure. Also Dapple dodge rolls are surprisingly difficult to punish.
Dapple Dualies Nouveau - I see these about as often as regular Dapples. It seems like it can create excellent pressure, especially for a short-range weapon. Toxic mist to block off routes/slow down enemies so you can move in for the kill. Then there's the Ink Storm, which can add to the pressure. You'll be getting Ink Storms with these things. A cheap 170 charge for Ink Storm with a painting weapon.
Dualie Squelchers - These are a good long-range alternative to the SS Pro or .96 Gal. It doesn't kill as fast, but it's much more mobile, it's much better at painting, and it's much more ink efficient. The sliding dodge roll is nice, since you aren't forced to stay still after doing a dodge roll. The kit is good for keeping an eye on your enemies. Point sensors to help lock in on your target or see if someone is going to ambush you. Tenta Missiles for doing better at seeking targets, and being a general nuisance.
Glooga Dualies - This is gonna need some buffs. Low damage output for a killing weapon and it can't paint. Its kit will also take some getting used to. I would hold off on using these until they're buffed. Either that, or just be much better than your opponents, and fight the opponents on equal grounds. I can almost see Gloogas as a training weight. Learn to be effective with these, then switch to another weapon and be a god.