Op you probably want something a little all mountain too just cause you've skied before. If you really want a fully symmetrical ski go for it but not too many cheap ones. Your gonna probably out grow them in a few years so size big. For a first time park ski just get something thats more on the cheap size cause your gonna beat hard.
Here something you might like.
Dynastar 6th sense spin 2011. Full twin tip. 119-87-109. This would kill park. 173cm and it's full camber.