Love love love love Hubbard! I used to nanny for an 18 month old until she was 3. We did swimming lessons the entire time - usually with Mary Beth. She was my favorite swim teacher, but they are all very good. Everyone has slightly different teaching methods so I think many people just prefer their first teacher since that is who they are used to.
I love how the teachers are firm - with the class I was in the kids are there to learn survival skills mainly, and also beginning swim skills - so this is serious stuff! They are firm with the parents on what they need to do to help their kids.
When i had my daughter we went to hubbard before she turned 6 months old for free! For the under 6 month crowd it's purely water acclimation - you won't be getting any amazing techniques, but it helps get the babies used to the water. It's $70 per month for one class per week, and we just can't afford it right now - but I am waiting and waiting for the day when we have some extra cash so I can enroll my daughter! Until then, I do the songs that I learned there in our pool and I still remember so many of the techniques from when I nannied so I apply them with my daughter.