Starting from today please forget about prestige, forget about uni ranks and forget about comparing yourself to others, otherwise you will regret it 10 years later like me.
Money is important, but (not financial advice) maybe investing in stocks? starting small?
I believe the most important thing is to do what you enjoy, typically (for me atleast) I enjoy things I am good at.
Are you better at Chemistry alevels or Mechanics in maths? Which do you enjoy more? Do you prefer making things? Do you find you would be able to do manual labour for long hours (I think the oil industry is really hard on your body)
Do note I am into CSi/ EEE so I cant comment specifics, and I keep failing also, so... But I think its most important to do what you enjoy and GET YOUR WORK EXPERIENCE
Also find out if its possible to transfer between the different engineering specifics, I think usually you have 1 month in first year to switch, but you can confirm with the staff at uni as you are applying