From a functionality standpoint, if you are not budget limited, I can't imagine why you wouldn't opt for a 430W. Sure, the older units can find locations, but the 430 does so much more. I don't know if you can get current databases for the M3, maybe you can, but the 430 is a very solid, can't miss upgrade. 480s might have more capability, but support might be lacking in the future. Why spend money on a dead end?? That's why I wouldn't put in a King 89/90 for sure, and would avoid the KLN94 just because I think the 430 is better. IMHO.
WIth WAAS, no more worrying about RAIM, plus you get mins like an ILS for a lot of RNAV approaches. THat's worth a lot to me, right there.