Olenna's a total babe. Being a Tyrell is probably the best thing that could happen to you if you were in Westeros. Powerful, incredibly wealthy, no 'omg DYNASTY' pressure like the Lannisters have, awesome grandmother...
[censored] yeah, Tyrells.
The only problem would be all the annoying men you'd have to deal with. Mace is nowhere near as bad as a Tywin or a Doran, but he seems like a minor jerk, and then you've got some of the Bannermen, like Randyll Tarly... I'd love to be a Tyrell, so long as I was allowed to spend most of my time with the Ladies of my house, and the rest of it doing my own thing. The Starks still hold the edge in terms of family love and happiness.
Edit: apparently the things porcupines are covered with count as a dirty word. Who knew?