I just read a very interesting blog post on Pew Internet recent study about their most recent findings.
http://www.socialmediatoday.com/SMC/140357

Insights:
Younger generations are moving towards Twitter
while Older Generations have embraced Facebook.

Good read. Based on my experience of these two social networking sites, I find Facebook more suitable if you are aiming for a way to stay in touch with loved-ones and do some activities with them such as games and applications.

Also both twitter and Facebook serve different purposes - Twitter is good for telegraph style 140 character shout outs. Unlike Twitter, Facebook is good to announce other happenings of your life in a non-limited fashion via text or multi media. Also, think about it, younger generations live by their cells during class or mall time so twitter may be more appropriate for them.

Facebook for me is really really helpful..It can give you a lots of traffics..

I also read on a site that older generations use AOL but I strongly doubt Gen Y do.