Where to invest time playing classic (classic only)? Era vs Anniversary

Hi Guys!

I am having the dilemma about where should I be playing the classic wow. There are no confirmations whether we can transfer chars from anniversary to era and going to tbc is it worth playing the char on anniversary now? Also, population on era seems to be very low so I am really confused where should I continue playing and for example level new characters etc so it wouldn’t be all for nothing and I can find people for dungeons and raids in a half year time.