I never go Piety -- not pre-patch and not post-patch. I guess I've tried once or twice, but always prefer Rationalism. It's not true that there isn't happiness in the Rationalism tree: The Humanism policy gives one
for each university, observatory & public school. Also, you get 15% more science when the pop is happy. Happiness is where you find it -- Tradition, Liberty, Freedom, Honor, Commerce all have good
sources. Especially don't ignore the Honor tree if you've got a medium-to-large empire: The happiness from garrisoned troops and defensive buildings adds up in a hurry.
In my games (I play nearly exclusively Emperor/Standard/Standard) I beeline Hanging Gardens (increased pop is good!), Notre Dame and Eiffel Tower (lots of happiness from these last two). Other wonders are OK, but I don't bust my butt trying to get any of the others, except perhaps The Oracle, Christo Redentor and the Sydney Opera House for the extra culture & free policies.
I used to (pre-patch) play exclusively for domination wins -- Total World Conquest (not just conquering the capitals). Now, with the post-patch happiness issues I go for which ever of the other victory types seems the most achieveable at the time. In my two most recent games (cultural & science wins, respectively) I had 96 & 52
at the end -- but this happiness can quickly disappear if you conquer a few large cities.