My answer would depend on what you're going to us it for.
'Spotting scope' suggests that you intend it for range use, and in that case one might think a shorter telescope with a tripod mounting-point would answer best.
I have a number of telescopes, and those that are most handy on the hill are the long, three-draw kind like the Gray, or the older ones made by Broadhurst & Clarkson, Ross and so on: the length makes them handy to steady freehand, or using your knee or a stick. They lack a tripod-mounting, though.
On the range, the shorter ones with a screw-fitting for a camera tripod are handier; I have an Optolyth 15-45x60 which does not draw out at all.
In the middle ground, I have an Optolyth 30x75 (one draw) and a Schmidt & Bender 15-60x60 (two draw) both fine for the range (shortish, tripod-fitting), but perhaps a little less handy on the hill because of the shortness when open, and the length and width when closed as well as the weight.
I've no idea about the Kowa or Minox. The Swaro is I think a single draw similar in dimensions to the Optolyth I've got. For range and hill, I would think that the old Nickel as described would do very well.
For decent s/h gear, I have used
www.kayoptical.co.uk ,
www.lcegroup.co.uk and for older ones in good shape, but at a price,
www.scientificcollectables.co.uk . At the moment, Kay and LCE both have a Swaro, and Kay an Optolyth. One must be mindful of getting a case or carrying-tackle, though.
The popular auction site also throws up these items from time to time,
sed caveat emptor!