If I understand your question, you have a choice of one of several one day excursions?

Its hard to answer which to choose because they are all worth seeing. Also, we don't know where your interests lie.

Both Caenarfon and Conwy have great castles. I thought the town of Conwy had a bit more to offer, but I had more time there. Both towns are not too far from Holyhead so I would think you get sufficient time to explore the castle and explore the town.

Porteirion would be a longer time to get to, but is a very different experience.

Snowdonia is captivating, but you really need to get out to experience it, in my opinion. Betwys y coed is a small village with resturants and outdoor shops. You could explore it pretty quickly.

If it were my choice, I think I would go with Conwy since you don't have time to hike. Great castle, interesting town with shops and other sites on the bay. Plus not too far from Holyhead so that you can spend leisurely time there.

How long are you in Holyhead?

I've never been a fan of Portmeirion, too theatrical, certainly eccentric and has nothing really to do with Wales. Although built in the early 20th century, it really resembles a folly in the Victorian sense. However many still find the place interesting.

Caenarfon Castle is both historically and architecturally one of Wales best castles. The town of Caenarfon, unfortunately, is not particularly interesting. Conwy would be my choice for the same reasons egnolive expressed. Snowdonia is wonderful for the scenery and Betws y Coed a pleasant spot but, I'd still opt for Conwy. Your decision probably is best decided by whether you want a scenic drive or if you want to visit a Welsh castle and explore Conwy.

Thank you so much for replies.
We're in Holyhead for a full 12 hours, but the tours leave mid-morning and are from 4 hrs to 61/2 hrs long. We'll only have time to do one excursion.
I'm sort of glad to hear someone say that they weren't especially fond of Portmeirion; it's the longest of the excursions, and since we're in our late 70's, we tend to get tired after 4-5 hrs or so.
I would LOVE to be able to do some walking/hiking in Snowdonia, but we also love gorgeous scenery.
We're not especially interested in shops and such, but we do love interesting towns.
Hoping to hear more!

Would you consider hiring a car- you could do all of that in 12 hours!

The excursions are "free" (i.e. built into the cost of the cruise), and we've always been very satisfied with Regent's excursions. Plus, as we've aged, we don't feel comfortable driving in other countries. (Had many wonderful decades of that.) Thanks for the suggestion though. So c'mon, Frances: Which one?!

We, on the other hand, really liked Portmeirion, partly because there isn't anything else like it in North Wales and partly because I'm a fan of The Prisoner.

Given the amount of time you have, though, I would go with Conwy. We enjoyed visiting the castle and strolling around town.

If you click on my screen name, you can find my trip report and a link to pictures.

Lee Ann

I understand you to say that you have a choice of two excursions-Caernarfon and Conwy or Portmeirion.
As you say you love interesting towns and walking then you really cut across both of these.
Conwy is exactly the sort of place I would head for in your position as if you are visiting the castle then afterwards the town is sweet and interesting to browse in.
On the other hand Portmeirion is unique it is just not Welsh. I love it and it is always first choice to take visitors to when they come and stay. You will travel through Snowdonia to and from Portmeirion.
Because I so adore Portmeirion I'd go there but Conwy also has its appeal
However as someone said recently on another post(words to the effect of)"I don't really like the question you are asking and so I'll answer the one you should have asked."
Are you adaptable- i.e. are you willing to branch out to try and achieve(for example) walking in Snowdonia?
Do you realise that not all of Snowdonia is at mountain level and there is good walking lower down accessible to roads?
Is 4-6.5 hours your limit because you will tire or because this is the length of the longest excursion?
Is this likely to be your only visit to Wales or just a taster?
Depending on your answer you can very easily do a little more-e.g. take the trip to Portmeirion, taxi from there to Beddgelert in Aberglaslyn- about 6 miles off the main road. Good walking here along the river and to Gelert's grave, sweet little village for a pit- stop. Continue by taxi through Rhyd-Ddu along Llyn Cwellyn and past the start of some of the Snowdon footpaths AND if you are still up for it see Caernarfon Castle on the way back!
Towns , Snowdonia, walking (and rain unless you are very lucky)
There are countless variations on this.e.g. See an English castle then contrast it with a visit to Dolbadarn castle just outside Llanberis-good place with good walking, and also Aberlleiniog castle www.aberlleiniogcastle.com near Penmon in Anglesey.
So much to do so little time to do it in.......