I have the Elrog ER300b, Elrog TM300b, Tak 300b, and a few pairs of WE300b NOS. I have not tried the Elrog ER300b-MO and modern WE300B. Also, I use these 300B for my pre, not power amps.
I was switching back and forth between the Tak and Elrog ER300b all the time as there were things I liked about each of them. Takatsuki has good details, more linear, and good depth whereas the ER300b was fast, open sounding with a very wide soundstage. The ER300b though in my system has a bit of harshness in the treble which I find a little too much at times.
Then came the Elrog TM300b, this tube has all the best characters of both the Tak 300b and Elrog ER300b, and more. Resolution and clarity are incredible while still be really musical. So much more micro details, nuances, and really dynamic. This is the best 300b I have ever owned.
As for the old school WE300b, I do enjoy them from time to time but they are not as neutral as the tubes above.
I have not tried the Elrog ER300b-MO but heard that they are also really good.