Serial and disturbed have done me quite well, have a had 5700x in the base game on serial and had $1565 win on a $22 feature buy on disturbed, have also had many 1000-3000x wins on serial in the features and base game.
Give Disturbed a good go, you basically just need a 4x wild in the middle and a symbol that goes all the way across with a couple of split symbols, pays massive if you can do that.