Hygiene is perfectly fine in Sri Lanka!! why would you think there would be a hygiene issue in SL???.Just book decent hotels and you'll be more than fine.and there are some great ones to pick from at very affordable rates.

you get great hill country (tea), beautiful beaches, wild life and ruins, all doable within a 2 weeks stay. enjoy!

I have been to both Sri Lanka and Vietnam and enjoyed both but they are very different. I much preferred Vietnam and have returned many times but I doubt I will return to SL. The diving in both cases is just OK (Vietnam probably has the edge) but probab;ly won't compare with the Philipines which is somewhere ( have always wanted to dive. The food is arguably better in Vietnam (a question of taste!) and I would say hygiene standards are better as well.

As you point out SL is a small country but it does take much longer than you would expect to get around. It does however lend itself to circuits of the main points of interest touring with a car and driver (independent travel is more difficult than in Vietnam.

Vietnam is much bigger and being a long thin country you could only hope to see the highlights in a two week visit travelling south to North or VV (Nha Trang is in the centre and the best place for diving). Alternatively, you could explore either teh North or the South in a little more depth in two weeks.

I've been to Vietnam and Sri Lanka, and I've investigated a visit to the Philippines. I think you would have a great time with any of the options. If you are serious about diving, the Philippines would rank the highest. They all have interesting cultural highlights. What is most important to you?

PS: I preferred Sri Lanka to Vietnam

I haven't been to the Philippines, but have been to Sri Lanka and VN. Everyone is different, but we loved Sri Lanka and plan to return. VN was interesting, but was not a "wow" for me.

I'd suggest you get guidebooks for all three countries, read and research and choose what appeals to you.

Food is a matter of personal preference. Hygiene is good in Sri Lanka, nothing to worry about.

I have a long trip report on my trip to Sri Lanka several years ago. If you click on my name, you'll see a list of my trip reports. Photos from that trip: www.marlandc.com/SriLanka/index.htm

I have been to all 3 and just returned from Sri Lanka.
We enjoyed all of them but Vietnam really resonated with us but as noted above everyone has different tastes. Philippines is #2 and Sri Lanka #3 for us.

-beaches, Philippines definitely has the edge, Vietnam not all good, and Sri Lanka has some nice ones but others are so so and some damaged by the tsunami of 2004
-food, Vietnam
-culture, Vietnam, Sri Lanka
-hiking, Vietnam, Philippines. Sri Lanka I am not really sure but it is very hot and humid. In Phil. the rice terrace area around Banaue has some beautiful areas for hiking and in highlands it is cooler.
- hygiene, you should drink bottled water in all 3, otherwise no big issues if using good hotels, restos. Stayed at some really cheap ones ($12) in Phil and they were fine.

Vietnam because of shape is a bit harder to do a circuit but 2 weeks is reasonable to see highlights. Sri Lanka is probably farther for you, 2 weeks is good, driving very slow though.
Phil is many islands so you have to pick 1 or 2 for 2 weeks. I loved the rice terrace area, as we really enjoy nice scenery.

Pick one then do the others next time.

Bon Voyage

I have been to the Philippines twice and I loved it for food, beaches, people, picturesque sceneries and many other things. It has got everything a traveler expects out of a tourist spot. Check it out here:
http://www.tripadvisor.com/Tourism-g294245-Philippines-Vacations.html

I was in Sri Lanka and Vietnam in 2011 and if I had to choose only one to return to this year it would be Sri Lanka. If you are concerned about hygiene because you think it would be like India put that thought out of your head. The culture is fascinating and diverse, the people are extraordinarily beautiful and friendly. The only thing I would say is the food is delicious but leans heavily on curry (if you don't really love curries) ...but there are other options for food as well.

If you're looking for more diving spots, choose Philippines - from beaches to culture to food, you can surely enjoy the trip. And I think Vietnam from this point can be scheduled for your next trip (except if you can't let go visiting any of its city). Sri Lanka would fit for the next mix that you're looking for. Just plan your flights accordingly and give enough days on each since for Philippines, you might want to consider staying in a Resort near to diving range(s). Have a great trip!