請問加那一隻DDR-2 667 1G Ram比較好呢

看見Mac Mini加了Ram後快了不少
http://www.macworld.com/2006/03/firstlooks/minifollow/index.php

所以想同iMac CD加Ram 但價錢都相差很大
ACEPLUS DDR-2 667 1G 1024MB / DDR2-RAM HK$643
OCZ Technology Inc DDR-2 667 1G COPPER 1024MB / DDR2-RAM HK$820
Century DDR-2 PC667-1G 1024MB / DDR2-RAM HK$950
Corsair Memory DDR-2 667 1G 1024MB / DDR2-RAM HK$820
Samsung DDR-2 667 PC2 1G 1024MB / DDR2-RAM HK$900
Kingston DDR-2 667 1G (512X2) 1024MB / DDR2-RAM HK$1,055

請問加那一隻DDR-2 667 1G Ram比較好呢
另加到1.5G還是加到2G好呢