Best Shuttle from Charles de Gaulle to Paris?

Even on the strike days some RER trains will be running from CDG to central Paris, although you will not know until last minute
I am also arriving in Paris on one of the strike days in May and if no trains will simply get a taxi. It is standard fare of 50/55 euros depening on if you are going to Left/Right bank of Seine

Depending on how many of you I would get taxi

On strike days, the taxi lines may be extra long. If by shuttle, you mean a shared ride service, I'd do something else based on my own three experiences (fool me once shame on you, fool me twice, shame on me, fool me three times and I deserve that for not learning from the prior two times). If by shuttle, you mean a private, non-taxi car service, I suggest one that does not have a prepayment requirement so if they do not show up, you do not have to chase down your money and I recommend Shuttle Inter (no prepayment and 55€ for 2 people) or Euro Jet Set if you have money to burn.

Last time I flew into CDG was a transit strike day, and we took the Air France bus (now le Bus direct) to Gare Montparnasse. It worked out perfectly fine. But it will be less helpful if you're not going to one of the designated stops.

I have used Paris-shuttle and Parishuttle before and have never had a problem. A cab would probably be a better way to go. Just remember that there WILL BE more traffic on these days and that you should leave earlier than anticipated.

We made a reservation with ParisShuttle (via TripAdvisor) for about $45/US (total for 2 people) for CDG to our hotel in the 1st arrondissement. I have some health issues that make it difficult for me to navigate the stairs in the subways with luggage. I can handle it without but not with luggage. If everything goes well, we’ll make a reservation for pick up at our hotel and back to CDG on departure day.

Our last trip was just before Christmas 2016, the trains were not running that day and we took a taxi directly to our hotel. He charged us 90 e. So we wanted to be proactive this time! Thanks for your advice and I’ll be sure to let you know how it went when we get back in mid-April.

Our last trip was just before Christmas 2016, the trains were not running that day and we took a taxi directly to our hotel. He charged us 90 e.

I believe that was before the new set fares of 50/55 euros from the airport went into effect, so that can't happen now as long as you use a legitimate taxi from the taxi line.

JHK,
so, how does that work?
Do you give them arrival time plus the amount of time to go through customs, etc?
Where do they meet you?

We had to give them travel information when we booked. The instructions from the shuttle service say we are to call them once we have our baggage. Even if we have to wait, this will give us time to use the bathrm, find an ATM for some cash and possibly a snack.

@jmlanza, For Euro Jet Set, you give them your flight information (flight number and ETA) and they meet you with a sign with your name on it just outside of where you walk out after getting your luggage. Then you walk with the driver to his car (I've never been met by a woman). I may be lucky because the vehicles have been parked very near the exit. For Shuttle Inter, they may meet you with a sign or tell you where to meet the driver, but you call when you arrive. Fair warning: since 2014, I have been taking taxis when I arrive or having my hotel arrange a car service and those have all been waiting for me with a sign.