Hmmm well these will obviously be JMO and will have huge generalisations but:
I avoid my local branch of Kew as the assistants in there are postively sneery, and you feel you are intruding. They also have very long, very loud personal conversations about there "facinating night out with Hugo Watsit Smyth". And they never have size 12 jeans.
I time my shopping in Next (of all places!), for a Friday as they have a fantastic woman, who charges round the shop for you, will hold stuff back and has an eye for what she thinks will suit you (and she's always right) I live in fear she will be promoted out of there as when she's not in the shop goes back to its usual lacklustre design. She makes it a shopping experience without being pushy (I fear I may have a slight crush on her )
Monsoon are generally good, and will ask if you want any help (if you do they're fab if you're browsng they discreetly dissapear.)
Boots girls are very smiley and if you've missed a 2 for 1 offer will hop off the till and grab another one for you.
Marks and Spencers are generally far too busy restocking to actually do anything. Though I think someones has a quiet word as the cashiers now actually deign to looks at you and talk rather than just putting a hand out for the card which was the norm last year.
Sainsbury's seem to have very motherly types and they will seek out stuff for you and guide you in the right direction.
Benefit make up girls will mob you, be generally very enthusiatic and if you give them your contact details ring you every month to try to entice you back.