I have several of each and they are both high quality cases.
The OtterBoxes I have use two locks to hold the lid shut and seem a little more secure than the Pelican cases. This is probably due to the distinct "pop" you can hear when locking each of the OtterBox's clasps. I'm not saying the Pelican cases aren't secure. It just seems to me that the OtterBoxes are literally bombproof.
The Pelican cases, however, have the Pick'n'Pluck foam inserts you can order to customize how the case contents are held. I have not been able to find such inserts for OtterBoxes anywhere.
All in all, they are both high quality cases and I would recommend either of them. They each come in differing sizes so buying some from both manufacturers should allow them to complement each other very well. This is what I have done and now I have many different box sizes instead of those only offered by one manufacturer.