Firstly, I dive APEKS TX40s and wouldn't change them for anything.
Now, before you buy there are many things to look for, your list is good, it will help you narrow down the manufacturers, but will not help you choose the model.
Firstly - decide what type of diving you want to do. This has a big impact of regulator choice. If you are doing mainly <60fsw in the caribean the reg will be different from somebody doing 150fsw decompression diving in cold, or polluted water.
So, for the first kind - you don't need any of the environmentally sealed regs, or those made of special materials (eg Mares titanium) designed for operation in very cold water - you can be sure that any of the regs from a good manufacturer will be more than adequate for this type of diving.
Reg choice becomes more critical in the cold water situation, here, it is probably best to talk to the local divers and see what they use.
A lot of people "buy the best" for life support, however, determining what the best is, amongst all the marketing is difficult. (For example don't be tricked by things like Titanium bodies, Ruby HP seats.....). For the majority of divers, "the best" is simply the one that you are most comfortable using.
When trying out regs, you will find the differences at low tank pressures for un balanced regs, or, more generally, at greater depths.
Jon T