From Heathrow to Waterloo Station 11pm or Later

No way the Tube will be of much use to you - it is asleep (except for Friday and Saturday nights) likely before you would get to it. Last train is at 00:18. Figure on at least 90 minutes getting off the plane, clearing immigration, retrieving luggage, walking through customs and out the frosted glass doors. It sometimes takes another 30 minutes. Or you might be lucky.

For 4 plus luggage, a man or lady standing with your name on a board as you come out of the frosted glass doors is probably a great idea at that time of night.

Safety is not an issue - the fact that you can whiz in on the traffic free M4/A4 right to your lodgings (don't forget to remind them how late you will arrive) in just a few minutes versus stop after stop on the tube; the Heathrow Express to Paddington is fast and you still need to get to Waterloo.

Get a private car. Plenty of folks here have had good success that way...

I'd say the Tube is safe. I worked at King's Cross and the old Thameslink station for many years and spent a lot of time in the Leicester Square area ...so I travelled on the Piccadilly line a LOT in London. What you have to remember is there are a LOT of people using the Tube to come from Heathrow so there will be dozens of people with their suitcases on any train.

As far as routes, there are three options (changing at Green Park, Piccadilly Circus, or Leicester Square for a connection). Personally I would change trains at Green Park and then get the Jubilee (silver) to Waterloo for three reasons. First off, there are only two stops between Green Park and Waterloo (the other two options have a three stop journey on either the Bakerloo (brown) or Northern (black) lines). Secondly, those stations you go through on the Jubilee (Green Park and Westminster) avoid Charing Cross (itself a rail station so there's more traffic - and it's the closest station to Nelson's Column / Trafalgar Square). And third, Green Park isn't as "night-lifey" as Piccadilly Circus or Leicester Square so the crowd will consist of fewer drunk office friends shouting "NOBODY LIKES MY SHOES" at their cohorts (hey, it's a big city and that's why we love it!).

The luggage is no problem as long as it has handles and wheels. Everything is designed designed to give you the smoothest time, and all three stations (Heathrow, Green Park, and Waterloo) are wheelchair accessible. It's 100% step-free access from street level to train level.

Now: time and day of the week. You're arriving late, you need to get through customs and get to the Tube ... so I hope you're arriving on a Friday or Saturday night because those are the only nights of the week the 24-hour Night Tube runs. If it is, you're "sound as a pound". If not, you'll be resorting to Plan B. I have no idea about hire cars (sorry).

If you miss the last tube (and you haven't stated your terminal of arrival, or as Nigel has pointed out, day) then for public transport you would have to fall back onto taking the Night Bus N9, which would be about 1.5hrs after a change at Trafalgar Sq. An experience certainly to be missed.

Thank you all for your very detailed responses and opinions. We are arriving on a Saturday night, so the night tube should be a possibility. Hubby would like us to take the tube to save money, but I have been nervous about that option. He and I will have to talk about it more. I appreciate all your help!