Just yesterday there was a news report on DRS3. Said that customers pay
some-odd million too much each year (combined

) because they have the
wrong Handy-Plan. Most people would be better off using a pre-paid type
account.
I, too, am light to medium user. However, due to the amount of data
transfer, I have a fix-abo.
With regards to "which is best for me", I suggest to shop around. As the
big names in tele-communications which of their plans best fit your profile
(UK calls and SMSing). Make your decision based on the offers and their
respective prices.
You may get the most information off the websites:
Sunrise (only available in German, does offer English per telephone call)
Orange (English)
Swisscom (English)