What lens would you choose?

The fisheye converter gives you a 15mm (35mm equivalent). SEL1018 gives you 15mm-27mm (35mm equivalent).

(SEL1018 + SEL18200) give you a range covering from 15mm to 300mm (35mm equivalent). This combination is very good for traveling: light and yet a wide range of coverage.

http://verybiglobo.blogspot.hk/2012/12/sony-sel-1018-f4-oss-vs-sel-16-f28.html

http://www.luminous-landscape.com/reviews/lenses/sony_super_wa_zoom_e_mount_for_nex.shtml

(SEL16 + Fisheye Converter) give you a curvilinear fisheye perspective, more profound than the SEL1018. But this can be achieved easily with post-processing.