For rustic charm/colour: Ascona (Maggiore), Morcote (Lugano) or Lake Thun in Sept?

Between Thunersee and its brother to the east of Interlaken called Brienzersee I would pick Brienzersee every time.

So for your three comparisons, why Thunersee?

By colour do you mean leaves changing or what is sometimes referred to as "local colour", or ambience?

Thanks for these 3 replies. By colourful, i meant colourful buildings like Bellagio or Positano - it's just so uplifting.
I said Thunsee only because Brienz itself looked quite small and I wasn't sure where else one would stay on Brienzersee, given the 'criteria'!
Interlaken is tempting but we prefer to always try new things.

Not in Switzerland, but take a look at Malcescine on Lago di Garda. It meets all your criteria except for the “cowbell vibe” which you are unlikely to find in a lakes die village, even in Switzerland (Think water purity issues).

https://www.visitmalcesine.com/en/malcesine

The Old Town around the castle has curvy cobblestone streets and lots of charm. And although this is Italy, German is as widely spoken there are Italian. It was the first language at the hotel where we stayed.

Brienz is famous for its wood carvers, and has the appearance of a village or town of wood carvers - plenty of carved wood everywhere, good clean air, a beautiful lake, the occasional arrival of a narrow gauge train or lake steamer - and a genuine steamship mixed in, the lovely Giessbach Falls and the victorian era hotel above, plenty of walking and even a steam train up the mountain.

Not much in the way of cow bells - you need to be up higher for that. Meiringen is just up the river a touch, with the actual Reichenbach Falls of Sherlock Holmes fame, you can climb up or down or take an ancient funicular, incredible walks around Meiringen and lots more too.

No colourful buildings - Swiss buildings tend to be earth colours and the natural colour of the wood.

Go to Italy for colour.

Thanks - yes good point about Brienz being lower down. Maybe Ascona is the answer. It does seem more Italian than Swiss in feel though, even though it's on the Swiss side.

While I'm here, has anyone on this thread tried the Loetschberg-Centovelli Express? We're thinking maybe could do London-Bern by train (7/8 hours), then the Express, which is Bern to Locarno via Domodossola.

But we want to reach Locarno AND get amazing train scenery all in one day, so would need to be leaving Bern by about 6/7pm I'd imagine, to get the daylight Does it run that late? I can't seem to find out on SBB and other sites.

From Domadossola to Locarno, it is the Centovalli Railway:

http://www.centovalli.ch/en/railway/centovalli-railway/

I've taken the Centovalli leg (Locarno-Domodossala) twice, though not recently. I enjoyed it a lot, as did my mother. I don't know how much of the Loetschental I've been through on a train. I once took a postbus high up the valley and walked back down. It was lovely, and I don't remember seeing any other tourists--but that was decades ago.

Understand a difference in terminology usage. In the UK "Express" usually means limited stops, faster than a stopping or semi-fast train. In Switzerland "Express" means that the marketing people have found a tourist orientated train which often makes every single stop on a particularly scenic line, or makes fewer stops but because the line is all single track with passing places still takes the same amount of time as the stopping trains, often for extra fare.

In other words, marketing speak. For example Bernina Express, Glacier Express, Golden Pass, etc.

The train you are asking about is very much slower than the fast Inter City trains which use the Basis Tunnel to burrow under the Alps between Bern (Spiez) and Visp and Brig. Your train is a 3 car long, or multiple of 3, primarily 2nd class train which stops at most stops up and over the mountains between Bern (Spiez) and Brig, continuing as far as Domodossola. Called Express because you can see the mountains and it attracts hikers and holiday makers for the stops along the way.

Ascona is a very quaint, and while it looks Italian, it’s very clean with lots of restaurants and walking along the lake front. You can walk to Locarno, which has a more big city look.
From either Swiss town town, you can take the ferry to any number of towns. The high speed hydrofoil ferries runs from both ends of the lake, but only a couple days of the week. But even the slower ferries are fun with stunning views.

You can purchase a two day (consecutive) Lago Maggiore express pass which includes unlimited ferries and the train from any train on the west side to the lake, to Domodossola, then over the mountain on the Centrovali train to Locarno. You can get off and back on the ferry or train to do a bit of exploring. If you could just do the two days on the ferries and skip the Centrovali, depending on if you are traveling on other scenic train routes.

We live in Verbania on Lago Maggiore and have done quite a bit of exploring up and down the lake. Happy to answer any other questions.

Thanks, that's good to know. I prefer the rustic feel and cobbles of Gambarogno but i know it will be too quiet after 2 or 3 days, yet Ascona, while busier and still top of our list, somehow seems a little predictable with the promenade and the elegant cafes. I think the word I meant to include was bohemian/arty/vibey and not too formal, and I'm not sure if another town on the lake fits that bill?! Does Canobbio come near?

The ideal outcome also is getting from London to Locarno in one day via a train route that is spectacular, and not msotly in tunnels. It's a tough ask I know! The obvious route is via Zurich and I'm clear from other advice now that it's not very scenic. Any other thoughts welcome!