This is a question that has many answers. Here is my opinion.
If you are a short or mid yardarge shooter, play your yardage. If you are 26-27 yards it usually takes a 98 or above to win that group.
Many calcutta's have a $20 entry fee with 30% going to shooter and 70% to buyer. This is a good deal as it pays great if you shoot well and your only in for $20.00
Zephyr is correct stating Lewis is a crap shoot. However, this has a tendency to pay big if you are the top score as many people play this option and you might get lucky on the Lewis score as well.
25's & 50's pay well if you can break a straight play these.
Open 100's are usually won with 98's and above.
Just my two cents....