The 2-pin plug is definitely the most common one around. Unless you want to swap cables between the Black and your Shure's, I'd probably recommend going 2-pin simply due to the ubiquity of it. Recessed will certainly protect the plugs more as @kubig123 said. It'll ensure a more secure connection and if - God forbid - the cable or plug ever becomes loose (usually it takes a good 2-3 years to do so), you have a safety measure ensuring the IEMs don't just fall off the connector onto the floor. Just keep in mind that when you're ordering aftermarket cables, you'll have to pick the recessed 2-pin plugs. Though, a solid 95-99% of cables these days come default with recessed 2-pin plugs, so you shouldn't have trouble there. I'd only recommend non-recessed sockets if you already have cables with non-recessed 2-pin plugs or you cable-swap often. Having non-recessed sockets will make cable-swapping much easier and reduce the risk of you breaking something trying to pull the plug out of the connector. But obviously, you'll have the drawbacks of less security and what-not relative to the recessed sockets. If you choose to go non-recessed, I'd still recommend you purchase aftermarket cables with the recessed 2-pin connectors, because those plugs work with both kinds of sockets, while non-recessed 2-pin connectors only work with non-recessed 2-pin sockets.