Aqualung is great company with worldwide distribution and very good regulators. It has been around longer than most other companies. Their Apeks regulators are probably the third best regulators after SP and Atomic. No issues with AL from an intentional point of view.
Poseidon: It has its own follower/cult and appears to be a solid company but it has a very limited distribution network and isn't a viable option for most these that are outside US and Europe.
Cressi: Its regulators and scuba specific products SUCK big time. Its customer service is even worse.
Oeanic/Hollis: I haven't had anyone I know praise their Oceanic regulators. I don't know of anyone who owns a Hollis regulator. They are a long time company with strong presence in the US and are now owned by Huish Group, the same owners of Atomic and Zeagle.
TUSA, they have international presence but not big. The regulators they distribute in my region are SP and Beuchat branded regulators. They appear to be a good company to deal with but certainly don't have the name or the distribution strength of SP and AL.
Halcyon: They have very weak presence everywhere but appear to make very solid BC's. Their regulators are SP rebranded regulators AFAIK. I'd just buy SP instead especially outside the US.
Atomic and Zeagle: Atomic has probably the best regulator out there. It doesn't have the robust distribution worldwide as SP and AL but they are some of the best products out there.
Dive Rite: Some of their products are excellent and of high quality but don't have international presence. They certainly don't have the international vision and the financial strength to be available and credible worldwide.
HOG/D6: They are a droplet in the US market and nothing outside the US. This isn't to say that they don't make good equipment, but they aren't international and have "opportunistic" presence in the international market outside the US. One wrong product or lawsuit may tear them down (they aren't the only weak ones in this list).