Killington has recently returned to the trying for the "first to open/last to close" policy of years ago.
All of this is weather dependent--a week of cold weather could get half the mountain open if they really wanted to with the snowmaking capacity they have.
Killington, Tremblant, Stowe, and Sunday River are your better bets.
Last year with colder temps Okemo also made mountains of early season snow, but the new lift install might hold up those plans until the shiny new lift is ready.
The North Ridge Triple with uploading and downloading on the K1 is probably the first lift you will be able to lap in VT. One advantage they have over "top to bottom" openings, like at Stowe or Sunday River, is the area is all above 3400'. Snow quality might be higher, and the new Peak Lodge would just be a stair climb away.
If you wait and the weather turns cold, you could luck out. If you want to play it safe, go to Killington, and buy a K-Ticket before 10/16 and you can get lift access for $61.