i weigh in around 160-170 6ft and i ride the 09/10 157 trs. as stated above, you could do either, but i see no reason for you to step up to the 159 unless youre riding a lot more deep days/ focus on mostly big mountain riding as opposed to any park stuff; even then, this board has a lot of float and will feel like a board in the 160s in pow.
ive found that the 157 is a good blend of stiffness (plenty of support for high speed groomers, steeps, big drops/jumps. etc.) and just a hint of playfulness for presses/jibs/flatland. really just a great board and ive ridden it EVERYWHERE from urban rails to deep pow days. it holds up to everything you throw at it, and long story short i love it. the only drawbacks i could think of (and this is splitting hairs) are
1.) there are times when i wish the board actually flexed a little more for me, but that's more a product of my riding style and need for a park specific board for those spring park/butter days.
2.) it eats through wax like crazy and is not the fastest base i have ridden. i feel like i almost need to wax before every session.