I usually park in the T1/3 long stay cark park and walk to the terminal. If you are lucky you can park just across the road from the open-air section of T3 short stay car park and pay a lot less and the walk is less than 5 minutes to T1/3. I usually follow links from
MoneySavingExpert.com which gives extra discounts with no credit card fees. I have also used the meet and greet service a few times. Dropping off the car is easy but you sometimes have to wait for the car on return.
I'm not familiar with T2.