Does MAC do the back-2-mac in the UK?
I like the MAC eye shadows - generally, they are very good and last all day. There are some that aren't as good as others (fall out, not very pigmented and so on).
Lipsticks from MAC aren't amazing IMO - and they taste awful. I prefer Guerlain, Chanel, Laura Mercier instead. Glosses are a bit meh IMO.
Blushes from MAC are good, I have loads of them.
Mineralize Skinfinish are nice and Mineralize eyeshadows are decent, although not as good as the normal eye shadows.
MAC brushes are very, very good. They last well, and mine are fine after years of daily use and weekly wash.
Never been keen on the skin care, including primers and strobe cream. Just doesn't work for me.
Most of the rest of their products are decent.
Nail polishes aren't worth the money at all. They are terrible!
My biggest problem with MAC is that the limited collections are so limited that they sell out very quickly - sometimes they are gone in a day or two.
Admittedly, I'm currently not in the UK, so things might be different for me, but they also keep changing release dates - so they'll tell me a date in the shop, then I'll come back on that day, and it's been changed again.
I don't have a lot of experience with Bobbi Brown - I have a couple of foundations from there, which are very good. And then an eyeshadow which looked wine-coloured, but for some reason it changes colour to blue on me 
A cheaper brand that does good blushes is Sleek. They are very pigmented, but they are very good.
Bourjois is good generally, and some of their products are very similar to Chanel - the healthy mix (serum?) foundation, the creme bronzer and some other ones.