Dear Angela, You asked a question:

year - Is the best word عام or سنة ? What is the difference?

There is a study from the Quraánic verses that shows a difference between سنة و عام;

Some Scholars said that عام is used to describe the good times in Quraán and it's using the Hijri calender, so it consists on counting days according to the phases of the moon, therefore عام is less than سنة in 11 days.

The same study said that سنة  is used to describe the hard times in Quraán and it consists on the Gregorian calender to count the days and they're 356 days.

http://www.youtube.com/watch?v=prQt13tgVPo

I really believe in this study.

And there is another study that said عام و سنة are used for the same exact meaning; they both mean "year".

http://www.awqaf.gov.ae/Fatwa.aspx?SectionID=9&RefID=21040

So knowing why you asked your question, I guess you can use any of them:) but the formal greeting for the new year in Arabic is:

كل عام وأنتم بخير.

Happy New Year -سنة سعيدة

good times - أوقات جيدة
good friends - أصدقاء طيبون
bright - مشرق

Midnight - منتصف الليل
year سنة they both mean a year عام - سنة
ahead -قادم

سنة سعيدة is the informal greetings
and كل عام و أنت بخير is the formal way of greetings andalso you can say كل سنة و أنت طيب

which means: Hope that every year you're good.

Happy New Year - سنة سعيدة

good times - أوقات جيدة
good friends  - أصدقاء طيبون 
bright - مشرق
year 
 they both mean a year عام - سنة 
however سنة is more informal
andعام is the formal word
ahead -مقبل 

سنة سعيدة is the informal greetings
and كل عام و أنت بخير is the formal way of greetings and it means "may you be good every year "


you're welcome عفوا!!

Happy New Year - سنة سعيدة

good times - أوقات جيدة
good friends - أصدقاء طيبون
bright - مشرق
year
they both mean a year عام - سنة
however سنة is more informal
andعام is the formal word
ahead -مقبل

سنة سعيدة is the informal greetings
and كل عام و أنت بخير is the formal way of greetings and it means "may you be good every year "

you're welcome عفوا!!

ممتازة