When leaving a job to either retire or take another job often requires a lot of homework on the part of the employee. There are many factors that will affect how or when you take your pension. Some of the items are marital status, financial circumstances and personal preferences just to name a few. So you need to find out if at all possible what the payout options are. For example can you roll the funds over to a new plan, possibly and IRA, or are you required to take a payout option? If you have the flexibility to roll over the plan make sure you work with someone who has experience in working with the plans to make sure the funds are properly rolled over. If you make a mistake in the process you could be subject to some unintended tax consequences. If you are required to take the payout option carefully examine all of the options before making a decision as once you make the payout decision there is no changing that choice.
I agree with Darrin… as he stated, the issue is complex and there are no do-overs. I generally recommend that people take a lump-sum if that option is available. Pensions suffered greatly in the most recent economic downturn and many are still in trouble. You may find this article regarding pensions useful. http://essigman.com/blog/?p=204
I am not a big fan of fee only advisors but in a case like this it may make sense to get an opinion from a fee only advisor. Advisors who bill based on how much money they manage tend to recommend you to roll over your pension in a lump sum. While that advice is probably true in most cases, sometimes that is not in your best interest. I would also recommend that you don't rely solely on your union for financial advice on an issue like this. They have an incentive for you to stay in the union and also keep your money in the pension account. Decisions like this usually have pros and cons.