I rate the Vectus G TBH, the new model is hybrid so you can replace the DVR now and then replace each camera as required later.
As for the differences between HD over Coax:- HD-SDI is digital, others (AHD/CVI/TVI) are analogue. Only HD-TVI can offer up to 1080p of the analogue options.
However, SDI being digital has a lower transmission distance compared to TVI. CVI is proprietary so I wouldn't recommend.