A lot of people who begin WA state employment later in life join PERS 3. PERS 2 allows retirement after 20 years of service at age 55; PERS 3 allows retirement after 10 years of service at age 55.
However:
PERS 2 is a defined benefit system. Your retirement benefits are 2% X service years X average compensation. Period.
PERS 3 is partially defined benefit (1% X service years X average compensation) plus another section defined by your contribution and MARKET performance. Yes, you do get to decide on which kind of investment you make, but it IS dependent on market performance. No COLAs for the defined contribution.
The state wants people to choose PERS 3 because it saves the state money.
Here:
http://www.icmarc.org/xp/plan3/pers/planchoice/keydifferences.html