well, doesn't mean more wattage give you more brightness , for example

X brand old model 10w give you 400lm
X brand new model 7w give you 550lm
so which is better ?

depends what specification they give you, for current bulb technology is > 80lm per what and usually is 270 degree, rather than 180 degree angle.

so if you have about 720lm for 8w, current is about RM 40++ per bulb retail with 1 year warranty. your price i assume is less than 550lm, 2012 technology