What I've been playing around with now that LW is gone, I'll get a PD then a LW. The PD really kicks ass combined with the IE, then the LW is the frosting on the cake. LW is now very situational for me though.
If they have a massively tanky team (which I've been seeing more and more) then I'll go IE then Madreds, LW, then PD. I've been playing around with going a blood instead of PD, since it almost seems like too much attackspeed, but again, the crit (52%) means I'm critting every other attack, which is awesome.
One thing, I was trying an alternate start that got me facerolled everytime and I finally agree with leirkov. Starting with a vamp is a HORRIBLE idea, unless your pub stomping. I've gotten it to work for me the way I want to maybe 2 out of every 10 games, and otherwise I just end up getting a dorans anyway, making it moot.
I've noticed that it almost seems like trist loses some of her effectiveness against a team thats 4+ tanks. Sure, madreds is good, but MR seems to shut it down.
EDIT: Plus, with vamps, you have to auto to recover health, pushing the lane and making it impossible to smash your combo on them (RJ, explosive, Ignite, ult) and many times, that combo wrecks who ever you hit it with, if you g et them down to about 3/4-1/2 life.