Were these the offering in your email from Amazon.com this morning . You must be a pretty good Amazon customer also ! (Heh, heh,heh)
I like Gergiev, I don't believe you have to worry too much about a bland Mahler set from him. The price of the set is pretty reasonable, but the LSO live production team is not quite as good as when Tony Faulkner was part of it. I'm not too familiar with Tennstedt, but I generally don't care for EMI remastering of what were pretty good analog recordings, they equalized much of the original SQ right off of the recordings. I like "Lenny" quite a bit, but the SQ of his various sets will probably be all over the place. Now if there was a Ivan Fischer/BPO/Channel Classics set it would be the "slam dunk" set for me.
Good listening & Merry Christmas