Scoreboard pressure application would suggest that batting first is the best idea, but if your batting is a bit weak then I'm not sure if it's worth the risk (what if you're 30-4 - will the lower order perform?, and would you set a commanding total or get rolled etc...?).
I think that fielding first and restricting them (seeing as you have a very good bowling attack...) would be the best idea as then you know exactly what you have to do to win.
For example game I played in today.
Oppo 254-7 in 47 overs...we managed to chase it in 35.5 (out of 36 overs - 20 from 6:30...) as we knew exactly what to do in the last 8 (60 needed from them...
)
All up to you though really - so long as you play well you should win mate