1

I'd have to say Thailand.

Sri Lanka has its good points, and ultimately any answer is going to be subjective. But, for me, Thailand has a much more varied and interesting culture, much more interesting architecture and archealogical sites, much better food, far better beaches and most importantly, far friendlier and accommodating people.

Less subjectively, Thailand is much better value for money. The quality of service you get in restaurants and hotels is far higher. It's also an easier country to travel in. The infrastructure is very good, but this doesn't mean travel in Thailand is sterile and bland. Far from it.

Sril Lanka often has the annoyances and hassles of India without the 'wow factor' to compensate.

Overall, I find Thailand a far more pleasant and interesting place to be.

Have a good trip wherever you go.

2

I agree with #2: Thailand, no question!
More to see, better to travel, richness of beaches and islands - and less expensive...

3

I don't think there is any doubt about it. Thailand is a much better destination by far. It has everything anyone could wish for. It is exotic, friendly comfortable and cheap. The food is out of this world. Transportation is cheap and easy. It has pristine beaches, and gorgeous hill country with fantastic architecture and cultural aspects.

Even Bangkok is an absolutely dazzling city with endless attractions and fantastic skytrains and subways and cheap metered taxis to go along with very reasonable hotels which are clean and offer excellent service. On the other hand, Colombo in Sri Lanka is a veritable polluted and disgusting dump where hotels and food are way overpriced as is everything in most of the country.

Twenty years ago, Sri Lanka was a pleasant destination. That time has long since passed. Today Sri Lanka is a complete waste of money for what you get in return.

4

Thailand. We were in Sri Lanka last March-April, and were disappointed at every turn. There is indeed, as was mentioned above, a near-total lack of "Wow". You could bundle the Cultural Triangle and Kandy, and they wouldn't compare to the Grand Palace in Bangkok, say nothing of the rest of Thailand's historical sites. The beaches are only very useful if you're a surfer.
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Sri Lanka is at that unfortunate point from a traveler's standpoint where it's too developed and bland to be exotic, and too expensive to justify its limited attractions. Large numbers of tourists who bought the hype now crowd the few and compact attractions, and they generally look pretty glum. I don't regret having seen it, as the food was good (not great), the people were pleasant, and the countryside is pretty, if unspectacular. But it's not a place I'd ever return to, and knowing what I know now, I wouldn't have bothered in the first place.

5

As everyone else has said you will enjoy Thailand more than Sri Lanka
Bangkok or Colombo there is only one winner especially for things to see and do
transport, food, accommodation, the beaches especially in Krabi province
are fantastic SriLanka used to be a good budget option but it seems
those days are long gone your money will go a lot further in Thailand
further still in Cambodia
have a good trip