My thinking is HQ because it is the rarest, and HJ for many reasons:

Still had GTS guards;
Nicest single headlight front;
Pre emissions engines expecially 1974 examples with no canister;
No ugly coloured stripes;
All had GTS rims.

HZ has it's benefits in RTS and chin spoiler though, but only had GTS rims for half of the run and got an uglier steering wheel. All in the eye of the beholder I suppose!

I think you'll find in the end that the Sandmans will follow the values of their GTS counterparts, with HQ being the most sought after by far, followed by HJ, then HZ and then the ugly duckling (but good value) HX. At least the HX Sandman didn't get the awful side treatment like HX GTS and LX SLR5000.