I would go with SENX because when they implement the site adding feature (if we will live that long to see it). It will be able to do everything what zeno can and more. As far as i know with zeno you can't set up schedules and different linking patterns.
As mentioned earlier, it really comes down to how you would like to spend your time. On one hand SENuke comes working right out of the box, no customization necessary. Its literally plug and play, so if your short on time, and dont want to go through a little bit of a learning curve, SENuke X is the perfect choice. However, the drawbacks are that it cant guarantee a 100% success rate with all of its tasks, and you are limited to whatever the software will allow you to do, and will require tons of updates to "stay with the times".
Now if you have a bit of time on your hands to spend learning Zenno, then you are in for something nice. With Zenno you can literally perform almost every task that SENuke X can do, minus the diagram designer. Web 2.0's, Social Bookmarking, Forum Profiles, Video, and anything else can be done with a 100% success rate, something you wont see in SENuke X.
Not to mention that you have the ability to create templates to perform WHATEVER task you want. I have a template that is set to only create 5 backlinks a day to my clients site (a slow, but steady drip). It pulls from a list of pre-defined anchors and URLs that I stored in the text file. Its set on a schedule to perform this task EVERYDAY (on its own), and then will export those results to my dropbox folder. Keep in mind that these are links of MY choosing, for a platform that SENuke X doesnt even support.
So in closing, it really just depends on what you value more, the short term, or the long term.