Honestly, I don't spend a whole lot of time accessorizing my watch to clothing. I usually just grab whatever strap I'm in the mood to wear. I like the idea of my watch standing out so if it clashes I'm totally fine with that. The platinum one I've had for like 3 years so its starting to show its age. It used to be my favorite and I'd wear it like 90% of the time but now its kinda rough. I've cleaned it so many times that its just not that nice anymore. So its been demoted to my cycling band. I wear it when I'm on the road bike or mountain bike.
I still wear the Obsidian one quite often, in fact I'm wearing it right now. But my go to straps these days are the Hasta / Silver, product red, or the midnight that came with my watch. I have a few others that occasionally make it in the rotation too.
I don't buy straps all that often. Usually I wait until I see them at Marshalls and buy them at the reduced price as I feel they are overpriced to begin with. Usually I find Marshalls has the most straps come in around late November for the holiday rush so I'll be on the hunt here pretty soon.