Both are different and for different purposes. Decide what you want to do first.
SEnuke - Will require lots of time and effort, you really need to write or outsource articles even to spin them, but the results are seen faster.
ScrapeBox - Less time and effort, but you will end up paying for proxies so factor in that cost too, people never tell you this but you will end up paying another 20-30USD for proxies every month. It has more of a learning curve and you will take time to master it and also it takes a while before the results too start showing.
In terms of performance, ScrapeBox all the way. Its light on the system and not much buggy. In the long run both will deliver but ScrapeBox has some blackhat elements to it which can be used to gain a lot of backlinks and linkjuice not possible with SEnuke.
Simply put if you are lazy and want less work then ScrapBox. SEnuke will demand time and effort on your part.
Finally I also used xGen SEO and it blew SEnuke away with its ease of use and also it is more powerful and lighter on the system than SEnuke so try that out too (has a 15-day trial).
I also saw Dukeware on this forum with a similar tool to SEnuke and while I've not tried it the demo/video certainly had me convinced and also its pretty cheap if you sign up as a beta user so check that out too.