For me:
The best:
Roses - Signature Truffle
Quality Street - Fudge
Heroes - Chocolate Eclair
Celebrations - Malteser
The worst:
Roses - Hazelnut Swirl
Quality Street - Strawberry Cream
Heroes - Dairy Milk
Celebrations - Snickers
Your ideal partner is the person who hates the ones you like and likes the ones you hate so you can get through a tub together without having to miserably suffer the worst ones once the good ones are gone.
It's tricky finding someone who doesn't think that the Malteser Celebrations are the best though.