The most important consideration is to buy a regulator you can get serviced.
So, buy a regulator that you can;
1) get serviced locally and,
2) get serviced almost anywhere if you plan to move in the future or travel extensively.
The TUSA RS340 is a good regulator and is essentially a rebranded Scubapro Mk 16. Tabata is the company Scubapro contracts with to make their regulator designs and once the exculsive rights expire, Tabata usually markets a nearly identical reg with different cosmetics through Tusa - which is "Tabata USA". And once the exculsive rights expire, Scubapro usually designs something newer to market that Tabata then makes for Scubapro. In this case SP has discontinued the Mk 16 for the generally similar but more evolved and fully sealed Mk 17.
Since the Mk 16 was discontinued recently you may be still be able to find one through a local Scubapro dealer at a really great price. You should also be able to find a Mk 17. The fully sealed design of the Mk 17 eliminates the only advantage a balanced diaphragm Apex first stage ever had over the Mk 16. I recently retired my SP Mk 20's for Mk 17's and in my opinion it is an excellent regulator. It is also available with a very wide variety of second stages.
Another consideration is the company itself. Unless you plan on upgrading to a new regulator every few years, you want to stick with a company with a track record of providing parts and service support for discontinued models. I would avoid Mares, given what they did when they acquired Dacor (discontinued parts support for all out of current production regulators.)
Scubapro and Aqualung both have histories of supporting nearly every single hose reg they have made in the last 40 years.
Scubapro goes a bit farther by making evolutionary design changes that can often be incorporated into older models. For example a late 60's Scubapro Adjustable second stage can be upgraded to use the same lever, poppet, and balanced chamber used in the current G250HP and when updated offers performance nearly identical the G250HP and S600.
Both companies are good choices for owners who plan to buy a good regs and only buy one once. Both also have wide dealer networks and can be serviced nearly everywhere.
Apex is an Aqualung subsidiary and you can probably rely on continuing support, but not all Aqualung dealers carry or service Apex regs.