My first speedo was an LRP indy 600 that went into my XX4 and stayed there for 2 years without one problem. Then I got into on road and purchased two V6's. Both of them performed flawlessly for a year and a half in mod TC and mod 4WD off road in very hot weather.
When I felt they were getting a little old they were sold and I decided to give Novak a try. Enter on Atom for my TC3 and one Cylcone for my XXX. Not one problem in over a year! I have two Quantum Comps for next week.
I can say that the replaceable wires on the Novak speedos is great and there reliablity was never a question for me.
LRP makes top of the line equipment and for me were just as reliable. If you take care of your car and your equipment you should be fine with any of the speedos mentioned.