I would recommend the Manduka. It's quite firm and provides a super stable platform. It doesn't stretch and squirm around underneath you like some cheaper mats I've used. When you apply force it seems to return your energy instead of absorbing it like spongier mats. It also has by far the nicest surface texture I've ever experienced - just the right amount of grip. My only complaint is that it's almost a little too firm. With my bony spine, some poses are uncomfortable (e.g. shoulder stand), and I often double layer it for ab exercises. Another possible downside is that is weighs a ton - great for permanent residence at your house (I treat it like a carpet), but not so awesome for lugging around. The price is sort of obscene for a slab of rubber, but with the lifetime guarantee, it's probably the last mat you'll ever buy.
I can't comment on the Lululemon Big Mat, but I have one of the old cheap ones (~2007) that is still going strong. However, another newer one around the house seems to be made of a different compound that is less durable. The material started to crumble off after a couple years.
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