The best time to go to the Caribbean is December to April, so definitely choose April. August has much higher rainfall and you're right in the middle of hurricane/tropical storm season.

I looked at Dom Rep vs Mexico vs Cuba a while ago.

Dom Rep has some lovely hotels from established chains such as Iberostar and Riu, great beaches, quite a bit to see and do, is great value for money and many people on this forum absolutely love the place. Downsides are that it's a very, very poor island and the infrastructure sometimes struggles to cope. This has lead to it having more than it's fair share of food poisoning problems, such as those at the Riu and Bahia Principe Resorts a couple of years ago, plus you need to take malaria tablets. All of which has kept the more established long haul operators such as Kuoni from featuring it.

Mexico - well we've just returned from 2 weeks at the Iberostar Paraiso Lindo and it was fantastic. Superb hotel with a lovely beach, friendly people, plenty of attractions on offer, even Cancun airport was a pleasure. Highly recommended.

Hi
I think it depends what you want from your holiday. I have been to both and of course there are pros and cons for each. Mexico hotels IMHO are generally of a higher standard but so is the cost of trips offsite. If you like to get out and about the DR might be a better choice ,once again depending on if cost is a factor. I found that Cancun was expensive in every aspect and trips cost around £60 pp ,beach fantastic ,water deep blue but too dagerous to swim in. I have stayed in Iberostar Costa Dorada ,great trips,waterfalls, horse riding white water rafting etc but yellow sand ,not white as in Punta Cana. The ICD had good nightlife where as the Ocean Sand/Blue where we stayed in PC had a beautiful beach but was quieter of a night and catered more to the Spanish tourists. I have to say though we had brilliant holidays in all three resorts

So as you can see there are many factors you need to consider, we are off to Cuba in 4weeks (first time) as we like to go to different places, so it will be interesting to see how it compares to other places we have been to.

Hope this helps

Debi

Personally, I would chose Mexico. Been to both places but have returned to Mexico and are going next week.......Cancun that is!!

If you want to see the real Mexico you need to go to the west coast,Puerto Vallarta.It is totally different from Cancun but a longer flight.The Riu hotels in the Dominican are good so I would go for the best price unless you specifically want to go to Chitzen Itza near Cancun.The resort itself is very Americanised.
August is hurricane season so I would chose April.We went to Cancun in April and had a couple of rainy days.Went to the Dominican in May,both times and only had rain at night.

We've stayed in Riu hotels in Riviera Maya, Mexico (last year) and Dom Rep (2004) and had fantastic holidays in both countries. However, we prefered the Dom Rep to Mexico. It's a matter of personal choice and if you intend staying mostly on the AI complex and not visiting much of the country, I'd go for the cheapest as stated in a previous post.