would you rather go to Varenna on lake como or Limione on Lake Garda for 2-3 nights oct 18

It's spelled Limone (without the 2nd 'i').

Both are nice, so I think that choice should be predicated on your overall itinerary.

If you happen to be in Veneto region, then Lake Garda makes more sense.
If instead you happen to go only around Milan, and not Veneto, then Lake Como makes more sense.

I prefer Lake Garda (especially Limone), but if you want to be surrounded by Americans, especially Rick Steves' followers, you should go to Varenna. At Lake Garda you will be surrounded mostly by Deutsch folks (and some Dutch).

I read in a different thread that you are flying out of Malpensa. Then you might also consider lake Maggiore (Stresa or Arona) for your last couple of nights before flying back home. Lake Maggiore is much closer to Malpansa than Milan is. 30-35 min. and you are at the airport from the lake.

I was in the region for some five days May of this year. From Milan I did a day trip to Lake Como by train to Varenna v.v.
I took the boat to Menaggio then to Bellagio back to Varenna. I liked Menaggio the most. Lake Como is lovely.

I think you can go to Switzerland (Lugano?) from Lake Como.
Heard good things about Lake Garda. I also went to Verona and did not have time to go to Lake Garda.