If a grower doesn't want to wait a year for a seedling to reach grafting size, just purchase a Day Avocado from Logees greenhouse, and graft a Mrs. Holland on to it in just a couple days. I bet I don't even eat one full avocado in a year's time. - Millet -

Yes they will although grafting percentages go down since it isn't pure Mexican race. I believe the Hass is cross between Guatemalan and Mexican race avocados.

Also do not confuse the tag/label "Product of Mexico" as meaning it is a Mexican race avocado!

Here is s good link from Perdue University.

http://www.hort.purdue.edu/newcrop/morton/avocado_ars.html

So what do I buy at the store, there are quite a few different types...

It seems like the commercial varieties seen most commonly in N. Florida seem to be the Guatemalan x Mexican hybrids (Hass predominant among them, sometimes a Lula, which tend to be greener than Hass, and with a significantly larger seed, some other miscellaneous ones) and the large, smooth-skinned West Indian (Florida) avocados. Pure Mexican varieties seem relatively rare. So between those, go for the GxM hybrids like Hass and Lula.
I forget whether someone has mentioned this already, but avocado rootstocks do not seem to make the significant differences that citrus can in terms of cold-hardiness. One guy I've talked with who has some experience growing them here says that he typically used Lula for rootstock due to the fact that the large seed produces a thicker trunk on which you can graft more quickly. He grafts low, plants the tree very high (i.e. digs a hole only an inch deep and builds a mound around the rootball) and once the graft is well established, builds the mound up around the graft using a very quick-draining mix.
I've had three trees, planted from 1-3 gallon pots, for two years - two Joey's grafted on who knows what and a Gainesville on Lula. All came through the two winters (relatively warm, with the occasional radiative frost - the lowest recorded was 19, but the spots where these trees were certainly didn't reach that) without losing a leaf, while some nearby year-old citrus were in various states of defoliation (mostly due to the fact that warm weather woke them up - they probably would have been fine in a more consistently cool winter with the same lows).

I have never seen pure Mexican race Avocados in the markets. I'm sure there have been but I have never seen any.

[QUOTE=Elsedgwick]Pure Mexican varieties seem relatively rare. So between those, go for the GxM hybrids like Hass and Lula.[/Quote]

Couldn't have said it any better.