I have been on OXPS since Feb 2007.
Pros: web interface, clean site, great customer service, wonderful educational opportunities, wide range of things to trade. I like the 'matrix' mode of how option chains are presented, and their online tools like StrategyScan and Dragon are quite helpful, too. I get great fills on stock and options trades at NBBO, and in that regard, I'm quite happy with them.
HOWEVER,
Cons: data feed problems, their Java-based xTend client is useless on the Mac for streaming quotes, xTend has been nonresponsive on both Mac and Windows during peak volatility periods, and their website 'page loads' can be slow at times going between chains-order-preview-submit process. Execution of futures trades via their web interface was horrible -- I quit trading the ES with them in February after me and a friend got burned for a few thousand bucks due to their systems....they credited our accounts once the problem was confirmed, much to our surprise and appreciation, though.
Both me and others have reported these problems in nauseating detail (screenshots and video) over the past year, and while those reports are acknowledged and some confirmation of problems are made, I see little actual lasting fixes to them, and these quirks continue. To wit: As I said, xTend on the Mac is continually buggy and useless for daytrading or realtime data. When xTend was nonfunctional for me and several other folks from 3:15 Thursday to EOD on Friday (both on Mac and Windows), that was the final straw for me.
I am very close to going with ThinkorSwim for my stock and options trading, for I have little faith or trust in the reliability in several core features of the OXPS platform and back-end infrastructure, and have given up hope things will be fixed anytime soon. How many profitable trading opportunities do you need to miss out on because of platform problems before you dump the platform and move on?
ETA: ToS' platform is Java based, just like OXPS xTend. Yet ToS' platform not only works, but feels and performs like a polished, precompiled native program, not something written in Java. Which makes me wonder WTF is wrong with the Java-based xTend at OXPS to make it slow, creaky, and buggy? Night and day difference in platforms!