Heading to the UK in September 2022. Considering a trip to the channel islands. Any advice? I'm starting and ending my visit from my friend's house in Horsham, so flying in and out of Gatwick. Would 3 days be enough for either Jersey or Guernsey? Which one if I was only going to one of them? I am travelling with my husband and 16 year old son and we want to do some light hiking.

There 4 worth visiting. Jersey is the biggest one and 3 days is plenty. Guernsey and Sark (you get the boat to Sark from Guernsey) is a day trip but together needs 3 days. Alderney needs a whole day.

These timings get you to everything so you can compress if you want to.

But then there is stuff like swimming with the basking sharks and stuff.

Three days would give you a nice taste of Jersey or Guernsey. My Trip Report has a section about my really fun visit to Jersey in 2012. (it is a very long report covering parts of Scotland, the Yorkshire Dales, Jersey, and the Queen's Jubilee/London . . . the Jersey bits start with post #102)

Saddest, weirdest, 'funnest', trip ever

If you decide to squeeze G and J into one trip you can take the ferry between which often ends up close to shore at the Jersey end. Worth the trip.

I personally wouldn't try to squeeze in both islands on such a short visit -- the driving is quite slow (speed limit is mostly 25 mph and some places slower) and there really is a lot to see.

We weren't thinking of renting a car but getting around on rented bikes. Is that feasible?

Speaking of Jersey (I imagine Guernsey is similar) . . Biking is fine but the distances are farther than you might think. But the bus network is quite extensive. So a combo of bikes and buses and you could see quite a bit in 3 full days. Staying in St Aubin like I did you could get buses to most areas of the island.

https://ontheworldmap.com/jersey/jersey-bus-map.html (the routes aren't straight lines like the map shows -- there are NO straight roads )

Many roads are narrow, I cycle all over and not thought of it as especially welcoming, but you could be right. Bus network is good

You’ll get more out of seeing Jersey or Guernsey if you rent a car. Cycling is great as well but in the short time you have, you’ll save time with a car and be able to reach the more remote places eg bays, coves etc.
Both islands have a lot to see, Guernsey is quieter and less developed.

There's more to see on Jersey and a better choice of restaurants and hotels. You will need a car unless you want to do shorter bike trips and with a three day trip you'll obviously see more on four wheels.

janisj, your mention of the speed limit brought back a memory of doing 100mph down 5 mile road, St.Ouens Bay after dinner at the Lobster Pot at Greve de Lecq, sadly no longer around I gather. The stupidity of youth!

The Lobster Pot hasn’t been around since about 1990 or so. A great restaurant & place to stay in its day.

IMO, Jersey, Guernsey and Alderney each have enough to see/do to fill 3 days. (Would the 3 days include any travel from/to the U.K.?) Do some research to decide which island best suits your ideas for this visit, and check the times of flights and/or ferries to see how much time you'd actually have. I prefer quieter, less developed spots and hiking, using cars/buses over cycling esp. when weather turns to fall. (How late in September is your trip?) Over multiple trips, I've come to enjoy Alderney/Herm, Guernsey and Jersey (in that order), but they all are interesting and very scenic.