Low volatility slots with 100% wagering contribution and simple mechanics clear bonuses most efficiently.
http://52she.top/forum.php?mod=viewthread&tid=191468&extra=
http://horsecity.ru/phpBB3/viewtopic.php?f=8&t=424324
http://forum.bandingklub.cz/viewtopic.php?f=48&t=1469157
https://debate.socialism.nl/forum/showthread.php?tid=233205
https://forum.zweb-apps.xyz/viewtopic.php?t=69274
http://forum.spolokmedikovke.sk/viewtopic.php?f=2&t=1119889
http://forum.spolokmedikovke.sk/viewtopic.php?f=26&t=1196480
http://forum.spolokmedikovke.sk/viewtopic.php?f=26&t=1051127
https://debate.socialism.nl/forum/showthread.php?tid=197418
http://treasureillustrated.com/showthread.php?tid=361382
http://www.lada-xray.net/showthread.php?p=228183#post228183
http://www.prepody.ru/topic68529.html
http://forums.shlock.co.uk/viewtopic.php?f=2&t=449696
http://forum.spolokmedikovke.sk/viewtopic.php?f=8&t=1119946
http://forum.bandingklub.cz/viewtopic.php?f=38&t=1313801
http://forum.spolokmedikovke.sk/viewtopic.php?f=6&t=1047246
http://strada.bielsko.pl/1_lubelskie/forum/4-zadaj-pytanie/582618-online-spilleautomater-renkespill#582618
http://forum.spolokmedikovke.sk/viewtopic.php?f=6&t=1155978
http://kiteonly12.free.fr/viewtopic.php?f=11&t=112148