Of course there are pros and cons to each option.

Kay.

Usually there are direct trains. But for some reason there is no direct train from my place to the airport on Sunday. This means that I have to take a bus to Rugby, and then change onto a train that goes to the airport. Sounds like a hassle.

Coach, goes directly to the airport, but there are no coaches later than 15.50 which arrives at 17.10.
My flight is at 21.20 FML.

Taxi. Comfortable, fast, direct and is 5 times the price of a train ticket. FMLx2