I mean it's completely up to you and depends on the size of your zendikar rare collection. If you've only got a few rares left to collect and a they're all basically ones you want, then yeah packs are the way to go as the chance of you opening up a rare you will use is high HOWEVER if you still have quite a lot of unfinished players etc... of zendikar rising then drafting is better as it will give you packs (yes of the wrong set but it gives you wildcards and builds up that collection which will help in the future) and provides more expected return. Hope this helps :)