I think that's a really tough question, one that likely depends on a whole bunch of variables you probably don't want to share with us on this forum, but in general, if the company's pension fund had long-term viability, it probably would be better for your sanity to take the monthly payout instead of the lump sum.
Large windfalls tend to bring a bunch of emotional baggage along for the ride, which can cloud otherwise sound judgement. Look no further than the average lottery winner, pro athlete, or celebrity for examples of sad outcomes. If you don't have the confidence to invest the money yourself you have to decide who to trust to invest it for you. There's stress that comes with watching large dollar denominated numbers fluctuate up and down with the markets in the short term, while still trying to keep a rational eye on the long term goal and deciding how much risk to take to make the nest egg last. That's one of the benefits of getting rich slowly, you tend to develop the virtues necessary for managing the wealth in the process of generating it in the first place.