[blimp]

suica, pasmo, pitapa or any other card, are just smart cards. you can "fill" them with either money and/or with a time period of unlimited travels between two destinations "定期券". you could get a non-smart card too, which doesn't really have a name more than the generic 定期券. i would say the train pass/定期券 is the most common for people working/studying at the same place 5days/week.

if you fill it with money, it will not give you any discount.
if you "fill" it with a time period it will be cheaper compared to taking the same trip twice a day for approx 20 times a month and paying for each time. depending how many times you do the trip it will either be cheaper to buy a train pass (commuter pass) or will be more expensive. i'm afraid i wouldn't be able to say when you would break-even

if you are a student you will get an additional discount on the train pass, however individual tickets will not be cheaper. tickets for kids (between 6 and 12 (?)) are half price.

on top of the above, some train operators also sell "multiple-trip-tickets" 回数券. one operator in osaka will give you eleven trips for the price of ten. i wouldn't however say that this is used by daily commuters though.