VESTS are locked STEEM that get voting rights, dilution protection (essentially interest approximately equal to inflation), and can only be withdrawn over a period 104 weekly payments. Something >90% (maybe much higher, I haven't checked recently) of the STEEM supply is locked up in VESTS.
Should we lock up STEEM purchased from Bittrex in VESTS? But if you do you won't get them back for 2 years?
"Over two years" not "for two years". When you transfer from vesting it schedules 104 equal weekly payments. The first is in one week.
As for what you "should" do, you will have to make your own trading and investment decisions.