I think 9 should be just fine. I-87 in that area (well, at least north of Lake George) is a rather pretty road too, in my opinion, and doesn't have overly heavy traffic generally.
My standard route from the Burlington area to western New York is basically US7 to VT 22A to VT 17 and across the bridge, and then NY 9N to NY 8 through the Adirondacks to NY 365 and then the Thruway as needed. It looks like you could continue on NY 49 to NY 104 to bypass the Thruway. Taking US 9 to NY 8 would work for you, and bypasses some of the steepest and curviest parts of NY 8.
The other poster's suggestions seem entirely reasonable to me, too.
The Lake Ontario State Parkway west of Rochester is open to RVs (unlike practically all the other parkways in New York), but has some comparatively low clearances and is in very rough condition. NY 18 along the lake is a nice road.