I own an Amplitrex tester, which is a fery good, albeit expensive, tester that tests at full plate voltage, which appropriately stresses the tube under test to give a realistic assessment of the tube. It is also idiot proof and simple to use, unlike testers that require one to look up the tube in a table and then manually set various dials and buttons as instructed by the table; you select the tube type from a menu, and all parameters are automatically set. The readiut not only gives real values (not an arbitrary scale), it also gives you the expected value and an interpretation of the values (strong, weak, etc.). Hook it up to a computor and it can trace the tube.
I have not tried the Etracer tester from Taiwan myself, but a big time expert who owns many different testers really likes it. It comes either as a kit or an already built unit. It has to be used with a windows computer. It traces the tube as well as provides numeric values. The expert said that its measurements agree very closely with that of the Amplitrex , but its tracing software is better and gives easier to read results. However, one has to set jumper wires to configure the tester to the type of tube under test, so it is not as easy to use as the Amplitrex. Still, this expert said he is considering selling his Amplitrex in favor of the Etracer.