This is a bit like asking if mp3 or wma are best for recording jazz. The advantage of AVCHD is its higher compression level at a given quality, but it comes at the price of requiring significantly more processing. The higher compression of AVCHD makes practical the current generation of HDD and SD-card-based HiDef camcorders that are far more convenient than traditional tape-based cameras.
With that said, the best HDV-based cameras appear to provide PQ that is very slightly better. I strongly suspect this is due to higher bit rates (even after accounting for the better compression of AVCHD) of HDV in tape-based systems because they have little reason to skimp on data rates given the capacity of (and ability to change) tapes and the relatively low processing requirements of HDV. In contrast, the higher data rates are more taxing on AVCHD due to pushing its processing needs yet higher and getting less time on their memory.
With that said, I personally find that the convenience, usability, form factors, speed and reliability of HDD and SD-based systems with AVCHD to overwhelm any tiny difference in PQ. If your sports shooting involves interactive replay for instruction (my son's basketball and baseball coaches do this), then tapeless cameras are even more compelling.
I would look at the camera - its form factor, optics, features, etc. - along with your specific needs when selecting the camera. The type of compression CODEC should be way down on your list (if at all) in making your choice. The only caveat here is that with AVCHD you will need a powerful computer alongside and that editing support is still not nearly as good as for HDV, though is improving. I expect these last factors to be irrelevant in the next year with another turn of Moores Law and improved AVCHD editing support.