Since you're a tec diver, I would recommend CCR over SCR. CCRs are virtually depth unlimited, unlike SCR. I would also recommend starting with a complete, working unit, unless you are very familiar with the unit in question - it will make the experience less frustrating and more enjoyable, and get you in the water and proficient much more quickly.
The meg seems to be prefered for cave diving (at least in your neck of the woods), but talk with people who have dived several to get their opinions. I know Gregg Stanton (
Wakulla Diving Center near Tallahassee, FL) has nearly all of the CCR units available to test dive in his onsite pool before you decide. He is also an instrutor for all of them and does a great job of weighing the advantages / disadvantages of each.
Since you are relatively close, I would recommend Gregg. Right now he is in the UK with Kevin Gurr, so he may not be able to be reached for a short while.