http://www.scotttradeelite.com/online_trading_documents/trading_execution/index.asp Scottrade shows execution speed is .74 seconds instead of the industry average of .6 seconds, but their price improvement is substantially better. See also: http://www.scotttradeelite.com/online_trading_documents/trading_execution/at_or_better.asp
TD Ameritrade Institutional shows excellent price improvement! http://www.tdainstitutional.com/brokerage/qualityexecution.html
This is all that I've found on IB so far: http://www.interactivebrokers.com/en/accounts/legalDocuments/timberHill.php?ib_entity=llc
Found Thinkorswim. It's quote amazing how albeit 1/2 of the orders for stocks are going to Citigroup, still, with the other 1/2 going to ATD (automated trading desk), how much ATD has made a difference! http://www.thinkorswim.com/tos/displayPage.tos?webpage=orderRoutingReports
EDIT: It seems though that Citigroup has acquired ATD! http://www.blankrome.com/index.cfm?contentID=43&itemID=145
Ok, found the best evidence regarding ATD: ATD ranks the best in frequency & in amount of price improvement! http://www.swampfox.ws/atd-ranked-best-overall-execution-venue-for-nasdaq-national-market-by-celent