I have had several moms do better with the classic than the lactina; it
may have something to do with the "suction curve" as someone else
recently mentioned.  However, I have discovered a couple of people who
have not received correct instruction on lactina pump use (rented from
someone else) who were using an older "standard" Lactina piston with an
"Advanced" connection kit.  This combo does not work! The suction is all
wrong. I always ask the mom to bring any kit parts with her when she
rents the pump so I can check to see what she has and give her the
correct connection kit.
Cathy Bastian, RD, IBCLC