A lot depends on the funding status of the plan.
Generally you will lose by taking a transfer as the risk of achieving the neceassy fund required to meet the promised pension that you would get as a deferred pensioner will fall on you.
If you stay as a deferred pensioner then the risk falls on the company. Hence their eagarness to get you to take a transfer. I'm not 100% sure of current figures but at the moment they probably offer you a transfer value that needs to grow at approx 7% pa to achieve what you would get if you stayed as a deferred. And this is based on existing assumptions such as inflation and mortality.
However , the advantage of taking a transfer is you eliminate the risk of the fund not being able to pay the promised pension.
You need more info about the fund and its funding position and the real likelihood of the company abandoning the fund without paying it up. Your age is also an important consideration as to how close you are to retirement.