Mondays, Wednesdays, Fridays. Heck, might as well add Tuesdays and Thursdays to the mix. 
Best
Available April 3: S&P 500 and E-mini S&P 500 Monday Weekly Options
S&P 500 and E-mini S&P 500 Monday Weekly options on futures will be available for trading beginning April 3. New Monday options will trade like existing Wednesday and Friday Weekly Index options, but they will expire on Mondays.
Available on standard and E-mini S&P 500 futures
European-style expiration
Initial expirations available: April 17, April 24, May 1, May 8; following the initial listing, two expirations will be available at any time
http://www.cmegroup.com/trading/equity-index/weekly-equity-index-options-on-futures.html?utm_source=cmegroup&utm_medium=banner&utm_campaign=equityoptions

Best
Available April 3: S&P 500 and E-mini S&P 500 Monday Weekly Options
S&P 500 and E-mini S&P 500 Monday Weekly options on futures will be available for trading beginning April 3. New Monday options will trade like existing Wednesday and Friday Weekly Index options, but they will expire on Mondays.
Available on standard and E-mini S&P 500 futures
European-style expiration
Initial expirations available: April 17, April 24, May 1, May 8; following the initial listing, two expirations will be available at any time
http://www.cmegroup.com/trading/equity-index/weekly-equity-index-options-on-futures.html?utm_source=cmegroup&utm_medium=banner&utm_campaign=equityoptions