Your A-Levels are ideally suited to Engineering, and if you want a job in high finance then they are just as likely (maybe more so) to take an engineer over an economist. If you want an Job in engineering though, then your chances as an economist are pretty dire. Not impossible, just very unlikely.
But the Engineering degree is an order of magnitude harder than the economics one, though there might be fewer essays...
Career prospects are definitely better in Engineering in my humble opinion. As for interest, well, if you don't find maths interesting, you're not going to have much fun in either subject. An Engineer is a problem solver who makes people money. An economist looks at what the engineers of the present are doing and predicts where the most money is likely to be made in the future, using tools developed by engineers. Economists may be in the higher paid financial sector, but as an engineer, if you go and work in the financial sector you'll probably be on more than an economist.
If you're getting the impression that this is a pretty one-sided argument being presented in this forum, maybe go and ask the same in the economics forum for a balanced response.
Stu Haynes, MEng