I think either method would work fine, and in practice you wouldn't have to worry about things like padding or alignment. The standard only guarantees that method 2 would work. Whether that's important to you is mostly a matter of personal preference.

I plan to use SSE or whichever intrinsics are available if the processor has it, so there's a chance that the data must be non-padded and 16 byte aligned to use SSE, for example. Sounds like method 2 is the way to go for me; I try to go for standards compliance when possible.

I think either method would work fine, and in practice you wouldn't have to worry about things like padding or alignment. The standard only guarantees that method 2 would work. Whether that's important to you is mostly a matter of personal preference.

I plan to use SSE intrinsics, and whatever else is available _if_ the processor has it, so there's a chance that the data must be non-padded and 16 byte aligned. Sounds like method 2 is the way to go for me; I try to go for standards compliance when possible.