For high end designer, I'd say the classics from Louis Vuitton are worth investing in, such as a speedy or a neverfull. And the price isn't too bad, compared to other brands.
If you're aiming high, go for the signature bags from each fashion house ( that appeal to you), such as the Chanel classic flap, Lady Dior, Hermes birkin/Kelly/Constance .
They have all stood the test of time and and are still popular. They won't date and you'll use them for ever. Remember cost per wear!
Avoid 'it' bags at all costs, high demand followed by low resale value, once you're bored if the bag, because everyone has it.
For other brands, go for quality leather/fabric and a style that fits your lifestyle (be honest with your self! ) and you'll love using it.
The Cambridge satchels are well made, funky colours and youthful.
Radley bags are well made for classic shapes.
Both brands are reasonably priced.
Words of wisdom..very good advice to avoid expensive mistakes.