Preference for Connecting options from Cinci to Lisbon

Some things that might be helpful to you in making your decision:

• In both cases, assuming you book as one ticket, you will not have to pick up your luggage at the connecting airport. You will also have to do a security check at both airports (sometimes at CDG you can avoid this, but you won't know ahead of time or have any control over this so it's best to plan as if you will.)
• If you connect via CDG, you will do Schengen passport control in CDG. When you land in Lisbon, there is no further passport control.
• If you connect via LHR, there is no passport control there. When you land in Lisbon, you will go through Schengen passport control there.

If the layover times are relatively tight, I'd probably pick LHR as you have one less thing to do at the connecting airport.

I personally hate connecting at CDG so would choose LHR if all other things were equal.

If you arrive at CDG you will go through immigration at CDG.

If you arrive at LHR, you will stay airside. There will be a security check, but no immigration. You will go through immigration in Lisbon where you should be able to use the egates. While I’ve missed connections twice at Heathrow due to delays (had nothing to do with Heathrow), both times I’ve been able to get on a flight the same day to my final destination.

When? I would avoid Paris during the Olympics. Safe travels.

Your easiest way would be to fly into Heathrow non-stop. Then catch a connecting non-stop flight to Lisbon.

Or you could fly United into Newark and catch a connecting non-stop flight to Lisbon.

We prefer to stay out of De Gaulle Airport.