(In your opinion) what is the current best new research MBE reactor I can buy?
The Riber Compact 21 (10 cell with 2″ heater) is an excellent new research reactor perfectly suited to MBE research.
(In your opinion) what is the current best second hand research MBE reactor I can buy?
Try to avoid systems manufactured before the mid 1990s. VG/Oxford made some impressive advances in the period from 1990-2004. The VG/Oxford V80 (1o cell with home/lift style manipulator) is an excellent second hand research reactor perfectly suited to MBE research.