None of them in my opinion. I despise the things.
From the cheapest £250 job to something in the tens or hundreds of thousands, all they ever say about a person is "look at me, I have some money to burn".
Anyone with money to give the government at will should seriously question what's important to them. I absolutely guarantee that if you spend the money on some books for young children and give them to a school in an underprivileged area you will enjoy far more satisfaction than having your initials on your car will ever provide.
I'm not against expensive cars, far from it, but I can't be the only one who looks at 'personalised' number plates with disdain.