Just giving some options. If OP wants to ride to work in normal clothes then a mountain bike, or any bike with an external derailleur and exposed chain, could be a bit more difficult. Just look at the thread on getting ready in the morning — it's complicated for people with recreational bikes and much simpler for people with city bikes. It's quite difficult to keep grease off your pants even with straps or clips to hold your pants in, completely a non-issue with a full chaincase.