This seems to be a hot topic

For those that don't know here are the basics

Pension

Pros
Company paid
benefit based on seniority
is a leg to stand on (which is not commonly available)
possible health care benefit in retirement

Cons
Probably a reduced salary (company profits have to fund raises and pension instead of just raises
Locks you into employer (benefit is based in part on years of service)
Less control over amount of payout

401k

Pros
reduces tax bill for you in current year
benefit based on skill of individual
You control the size of your own benefit
Not tied to company performance
You can take 401k with you to another employer or roll over into an IRA if you want another job

Cons
reduces current income
need to be educated on how to invest
dependant on employer plan choices