Reply to Controller Recommendations

Hey guys. I was just looking for some recommendations. I have been performing as a mobile DJ for about 3 or 4 months now, using a Numark Mixtrack Pro - performing simple mixes. I am now looking to take my performance up a notch, and I was wondering what those of you who are more experienced would recommend to buy controller wise.

Right now I am looking at an S4, but have also considered maybe buying a novation zero sl mk2 to use in conjunction with my mixtrack.
(http://www.novationmusic.com/product.../zero_sl_mk_ii)

Of course I am looking for portability, durability - as well as the longevity of the product (How long I am going to be able to use it before I need to upgrade).

Cheers,
Harry