Really depends on what makes your heart sing and what you're looking for but I'd go with Cartier hands down.
Both of them are at premium price points because they are luxury brands and that's what they do.
However, in terms of design, the Cartier love bracelet is a classic of the house. It may be an extraordinary price but at least I'm paying for a design that is unique to the brand.
I can buy diamond studs from my local jeweler or buy diamond stones and get them set in a pair of earrings. Doesn't matter where they're from because they are just a simply a stone set in studs. There's nothing particularly unique about the design that would tell me they are Tiffany.
agree with above....paying through the nose for premium designers is primarily for their design. Unless you're talking about huge carats, I think the premium cut and color of design house diamonds can be matched by a good reputable local jeweler.