If you grow from seed, you'll get some natural variability in the avocados you end up with. I don't know how much variation there is in avocados. But I know in Spain at least, the avocados are all grafted. That way, you know what fruit you'll end up with.
Not sure what you mean that you'd rather have a whole tree.
I have grafted some apple trees here so that some of them have several varieties. If I decide if rather have just one variety, it's just a matter of cutting off the branches that bear the varieties you don't want.
Google top working trees. You keep the roots and switch varieties... Quicker to get fruit and more predictable than growing from seed.
