Originally Posted by Some person

They have to offer "re-routing, under comparable transport conditions, to [your] final destination at the earliest opportunity" but it is untested what "under comparable transport conditions" means so it is unclear if a competitor offers "comparable transport conditions" or not. If you insist that a competitor offers "comparable transport conditions" you'd probably have to book the flight yourself and claim back the money by suing Ryanair, which is risky as you won't know if the court will rule in your favour. There is a demand by the UK regulatory body to airlines operating in the UK to clarify when you are entitled to rebooking on other airlines, implying that there are some situations where airlines are obliged to rebook on other carriers, but the CAA's interpretation appears to be untested.

Do not forget to claim denied boarding compensation. Ryanair is due 250 or 400 euros depending on the distance of the flight.