Chronos my experience with both stores is about equal. Both have wonderful customer service. If either of them don't reply fast its usually one getting swamped and the other going to cons. (obviously that's not happening now due to Covid)
When it comes to shipping it's really hard to choose. I don't usually have an issue paying the higher rates in moderation so this is a personal choice. The increased costs have made it difficult for both of them to nail down a precise charge until release. At one point Todd was going to do away with even showing the charge on the order page till release.
For me Spec Fiction edges out SC just a hair because I've asked Todd to put up P1 pieces during the Sideshow debacle and he usually would. He also puts up EX/Bonus pieces more so than Secret Compass. Secret Compass is the official Prime 1 distributor in the US. That means BBTS gets their stock through them along with a few other shops. I'm still working on Sideshow to find out how/where they are getting their stock or if they have a deal in place with P1.
Three experiences I've had with the companies. I purchased the Matrix Studio Shockwave from SC. Mine had 5 broken pieces. Matrix Studio wouldn't do anything so Shane stepped in and gave me a partial refund. My XM Optimus has an electrical issue in his hologram arm. Todd asked for a new one. They shipped it with a few other replacement parts and they all came damaged so he sent out for another one. I'm still waiting for it almost a year later but so much has happened and it's still being taken care of. More recently I paid for my XM Megatron shipping on Friday at SF. In the thread Cletus and I paid at the same time and he received his first and mine hadn't even shipped. I messaged Todd yesterday and he took care of it overnight.
Both owners can be contacted anytime. I trust them both but I would personally use Spec Fiction. I also have more preorders with SF and I have received more pieces from them. Also Todd has a payment plan which is pretty decent.
*Chronos check out the XM 1/6 Wonder Woman thread last page. That's all you need to know about Spec Fiction.