Pros
The people at TriNet are amazing to work with. The work is interesting and you are constantly learning new things. It is possible to make lateral/cross-departmental moves to gain knowledge and experience. Depending on your position, you may be able to work remotely at your manager's discretion. The benefits are good and they provide fun activities/food for employees at least once a quarter. They are also active in the community and you get 8 hours of VTO every year.
Cons
Things have changed since TriNet became a publicly traded company and not necessarily for the better. Work/Life balance is talked about but people feel obligated to put "Life" on the back burner and people find themselves frequently working nights and weekends. TriNet has grown at a very fast pace and it doesn't seem like the executives have a clear plan except for people to work harder/longer. You will get compensated at the lowest rate possible and it is difficult to get promoted up unless you are friends with the higher-ups. How hard you work or how much you contribute gets verbal praises, but money does not get put where the mouth is. Upper management diversity is non-existent. We're talking mostly and "old boys" network. Any strong female leadership leaves to pursue their goals else where. Compare TriNet's leadership team to ADP's leadership team available on both websites to see the difference.