I'm currently on Manulife LifeReady 20 plan and considering if I should drop the plan and take up AIA Pro Lifetime Protector?

You should really consider your needs before dropping your Manulife plan as the 2 solutions that you are talking about are different. Manulife is a Whole Life policy whereas the AIA one is an Investment Linked Policy

You should state your consideration for switching and then we can judge if it's sound.

Do list your sum assured, premiums, surrender values at differing ages as well and for the Manulife plan, when you purchased it and how much premiums you've paid so far.