I would have to say the s90v/cpm154 is most collectible. It has least number produced at something like 300, and it was spydercos first run with the clad steel. followed by the s90v with 600 made ,then by the M4 with 1000+ if i remember correctly. Thats how I'd rate their collectibility as far as just CF models are concerned.
If anyone reading has access to edit the spydiewiki and accurate information, I'm pretty sure it is not correct about the number of Jade M4 paras made, showing 2200 plus 11 in CC #s so it should be edited.