""in the same Brant some model has higher size with lower price, but some cases sizes are big but the prizes are low. so really i confused""

what are u confused for? both of ur sentence means the same.

Samsung & Sony are at best competition however, u may not know that Sony buy their LCD Panels from Samsung. so, do u think samsung would be giving them the best to beat themselves?!

if u are very keen on getting the best, ofcourse the LED from Samsung beats all.