Getting to all three is expensive and timely unless coming from the islands (Aruba, Trinidad, etc).
I lived in Suriname for two years, 2010-2012. I can tell you that it is safe and relaxed and Paramaribo is worth seeing if you are that kind of traveler. The people are lovely and English is spoken by almost everyone in the capital. It is a rapidly developing country with a lively political culture (the former dictator is now the fairly elected president - I observed the elections in 2010). It is a unique place with a unique history, more Caribbean than S American, yet not quite, given the lack of cricket and the Dutch language. Unless you are going to the jungle you won't need more than a few days there. Eco tours are great but can be expensive. Plenty of decent food/restos and nightlife, movie theater, etc to entertain. Interesting architecture as well.
Guyana kind of sucks. There is a real lack of infrastructure, restaurants, hotels, etc, and it is relatively dangerous to get off of the beaten path at night in the G'town. I have not personally been there, which says a lot since I stood on the opposite shore and gazed across a few times, and I love to travel, but just wasn't worth the effort! It takes 10 hours to drive capital to capital mostly due to the horrible roads. OK, enough of that. If you do go take a charter flight to the waterfall which I hear is wonderful.
Fr Guyana is an overseas department of France, so as others have said the GDP is a bit higher, etc, but it is an illusion. The numbers are inflated due to high subsidies and sparse population. France and EU pump money in there because the European space station is there - b/c of proximity to the equator it is cheaper and easier to launch satellites into orbit. If you can get a tour there do it. One of the best side trips I have ever done was a all-day sail boat ride to the former Devil's Island prison colony where you can swim off the boat right to the islands and see where some famous people were failed - Papillon and Dreyfus. Really one of the most interesting things I have ever done and such a lovely trip out to the islands. Do it! Downside to Fr Guyana is it is unreasonably expensive, and Cayenne is the absolute most boring capital city I have ever been in on a Sat night in my entire life. After 45 mins we found one bar open and it was karaoke, so the night wasn't completely lost.