Scubapro MK25 Evo/A700

Combining the highest performance first stage on the market with an unbalanced second stage produces basically the same performance as a MK2+R195 for double the price, while not having the bullet-proof and easy-to-service advantages of the MK2. For 99% of divers, the MK25 should be paired with an S600 or S620 (try both and see if you like the smaller 2nd stage). If you aren't buying a package for some reason then they can also be paired with an S360 or S560 because they're basically the same thing as an S600 with different materials. If you're diving in fresh water colder than 2C or sea water colder than -1C then ignore the A700 and buy an Apeks regulator instead (but buy the A700 if you think it looks cool - that's basically the advantage if you're not diving under ice).

Based on manufacturers you mentioned and your interest in going into technical diving, I'd probably lean toward the Scubapro MK25 with A700 or S600 second stages. A rotating turret really has it's benefits, especially with a twinset. For a BP/W setup, Scubapro has the X-tek line of products which are excellent quality though they won't be as economical as the Dive Rite setups . Regardless of which BP/W you go with, I'd highly suggest a steel backplate so you won't have to carry as much weight when you dive.

I dive two MK25 / A700's ... great performance regs that are nice and small and also great in cold water ... but if I was to replace them, I would probably go to the S600 for the easier access to the diaphragm / internals of the second stage ... the A700 requires a torx driver and is really not serviceable in water. Performance wise they are very similar to identical. I would not spend the extra for the S620ti. Take that money and get a matching second stage or an S560 ...