Can't comment on the models you cite here, but I use the Mares Abyss as my primary and the Axis as my back-up on my BCD-single rig. Top regs mate - never breath wet and you can dive in any temp, any trim (face to surface) and they've never let me down. Very easy and smooth breathing.
The above said, for my twins rig, I've just bought a pair of JetStreams; I'll be able to comment shortly after I've had them in the water. Hope this helps.
Hi Paul, Mares regs are superb, ask Dave Baugh. I have the Rubys which are for sale. Great for warm water but below 10 deg need cold water kit. They are very finely tuned and so when removed during skills will start to freeflow , not seriously but annoying and puts students off. Hence I bought regs designed for cold water and dont flow off when taken out so ideal for teaching, the Apeks TX 40. Just my thoughts for you to kick around.