Well, the actual panels are made by the same manufacturers (LG, Samsung, etc) just badged up/put in different enclosures according to braynd. A bit of research will reveal that X model by X brand uses the same as Y model by Y braaynd.
Hannspree make their own screens, they got fined last year for being involved in a price fixing racket with LG, & Samsung.
The advantage of buying a “premium” (i.e. Sony/LG/Samsung) brand LCD telly is that you stand a better chance of getting a decent picture. You do pay a price for the name, but usually you get a better telly too.
Things to look out for are ghosting in fast moving scenes, which can be annoying (especially playing games on PS3 or watching sports), blacks not being very black (washed out grey), and scaled images from standard definition signals like DVDs or freeview/freesat/virgin looking blurry, jaggy or oddly pixalated.
Everyones eyes are different, and I’d suggest going to somewhere like Richer sounds, or curries, and having a look at the pictures on the screen.