What is more important Core Clock or Memory Clock?

You can only compare clock speeds on identical cards. You cannot compare clock speeds on different models, because each card has a different architecture which is (much) more fundamental to how the card performs than clock speed.

The reason the 5650 performs so much better is because it's a more robust, powerful GPU architecture than an integrated 4250. Clock speed does not have a direct correlation.

The only way to find out what graphics card you should purchase is to read a lot of GPU reviews, or ask on forums like these so that people who have read lots of GPU reviews can give you purchase advice.

but if its the same card like
http://pcpartpicker.com/part/zotac-video-card-zt6110210...
or
http://pcpartpicker.com/part/evga-video-card-01gp43652k...
one has a faster core but one has a gig more memory im assumining memory would win? both are 650ti's.. but lets say both havce 2G but one has a faster core clock and one has a faster memory clock which should i go with?

amount of vram does have an effect in those cases when the game needs more than is available... These days more and more games can go above 1gig limit even on the common 1080p resolution, some games (with mods) can go above 2gig. But if the card has like 6gigs of vram and all your games only use 2, the rest 4 wont do anything. Or if the card lacks the grunt to actually run a game at high enough settings that would consume lot of vram at playable framerates.

Slight variations in clockspeeds can be overcome by overclocking the card yourself, usually factory OCs are very slight anyways. I would go with the one that has better cooler (assuming the cards are otherwise similar and there have been reviews to show which cooler is better) and/or warranty.

ahh ok thank you

Which the best, according all of you :
Digital Alliance Radeon HD6670 2GB DDR3 128BIT
vs
Sapphire Radeon HD6670 1GB DDR3 128 Bit?
After you choice, please explain your motive.  

Well I personally don't run any AMD cards the reason for that are, I feel the architecture is lacking all around. now to your ? when you are looking at two card that run at very close speeds and performance lvl's but one has more RAM I would always go for the more ram do to the fact that the new GEN of games can use it. so I would say the HD6670 2GB DDR3 128BIT, is the way to go. but a asus gtx 660ti will out perform both of those card in huge amounts. like a big bully stomping on a little guy.lol, 660ti price $250.00

Thanks for your answer & suggestions, trickedout. Any body have the others answer and reasons?
 

Thank you for your answer bro.
But if you only have two options (because something), Digital Alliance Radeon HD6670 2GB DDR3 128BIT with memory clock 667 MHz and Sapphire Radeon HD6670 1GB DDR3 128 Bit with memory clock 800 MHz, what do you choose? 

Thanks so much for the answer & your suggestion. Maybe i'll rethink to buy that stuffs.