Both can be amazing pieces if you find what YOU need/prefer for your set-up; but I prefer spiderwood if for no other reason that it seems to be used less and therefore tends to give a scape a bit more individuality versus traditional manzanita (which can be absolutely stunning but has somewhat become the norm and therefore seems a bit overused/overpriced imo - although someone here did resurrect recent thread recently about couple good place with much better prices for manzy et al, but I'm in no shape at present to search those links at the moment, heh) . But I;m one of those that thrives on individuality and thinking outside the box so always looking for different options to manzy. Nevertheless, I would jump on a nice piece of manzanita if price is right and it meets your design/aesthetic preferences. Some of these can still be the most twistedly branched, beautiful,complimentary pieces within the art form.
Others I've been giving considration, and just as beautiful (eye of teh behoulder I guess) are Ghostwood, Grapewood and something I cam across recently called Melaleuca. None of these or the aforementioned are necessarily cheap so best advice is to ask questions on the supplier, get pics,dimensions and make sure you're getting what you prefer. In the end, that's all that matters as I'm sure your poll will no doubt have different opinions, as I'm equally sure my post will receive some sort of contradictions as well. But that's the name of the game and each to their own. Opinions are good but no matter what anybody says, trust your own instincts and go with what suits your aesthetic approach.
Also perfect time of teh year (at least herein the southeast) to skower a few parks,rivers,creeks for fallen oak, hickory and some of other hardwood varieties for some quality pieces. Nothing like the thrill of the hunt for that perfect piece, plus it's free. I'm planning a dw hunt this coming wkend and packing a few bags of dried oak leaves for possible future blackwater endeavors.
So, yeah, long-winded response but I'll vote for the spider