First car needed for motorway driving

I don't know a lot about cars and I'm looking to buy my first car. I have been offered a job that requires a 90 mile round trip to and from work five days a week. I'm in my mid twenties and i'm looking for something that has a good MPG thats Not to expensive and wont cost a fortune to insure.

I'm told that a diesel car would be more suitable than a petrol for the mileage i will be doing Is this true?