Ibuprofen has greater anti-inflammatory properties than paracetamol, so if your pain is an inflammatory one e.g arthritis or say twisted ankle, then Ibuprofen is the answer.
If your pain is less inflammatory say acute sciatica, the paracetamol may be a better choice or indeed combination of the two as suggested by bobbisox.
ummmm also has a point in that over a period of time, you may find the right analgesic that fits there bill