Yes, certain varieties may be better for rootstocks for specific situations but since you’re in NYC, the benefits of the Turpentine rootstock may not be applicable to your growing situation.
Since you mentioned you wanted practice on grafting, Monoembryonic seeds generally have a thicker stalk upon sprouting so you won’t have to wait as long to begin practicing. Whichever type of seedlings you decide to use, just know that young seedlings are extremely tender and fragile.
They are very juicy and soft like a bean sprout.
If you go to the supermarket to pick up fresh fruit, make sure they are not irradiated. Hot water treated Mangos will sprout but irradiated fruit will not sprout, at least they haven’t for me.
I like to use Kent, Haden. Tommy Atkins or any other Monoembryonic varieties other than Keitt and Julie which tends to grow very slow for me.
Here is a link to more information on Mango rootstocks in case you’re interested
http://tropicalfruitforum.com/index.php?topic=20816.0Simon