When I first thought about teaching English in Thailand, I spent months researching programs and reading reviews. I was so scared I'd pick the wrong one, as there are many out there that are only out to make money and provide little support after they get your payment. Greenheart Travel's Teach in Thailand program is nothing like that, and is worth every penny you pay! I did so much research, and I promise they are the best out there.
Sara at Greenheart (she's amazing!) is the Thailand program manager, and a young twenty-something who has also taught English abroad. She's so friendly, positive, and passionate about helping participants have an incredibly meaningful experience. It's really easy for you to relate to her, and vice-versa because she's been in your shoes. She probably answered a hundred random questions I had before I even applied, and was always prompt and honest in her replies. And even now that I'm back in the States, she has kept in touch and I still feel a part of the Greenheart community.
Some things that stood out about Greenheart: They are a non-profit, they have a reputable Board of Directors, their program managers are all young adults who have been in your shoes, they have an actual office in Chicago, they are organized, honest and want the best for their participants.
It's important to understand that Greenheart Travel is the recruiter, and they work closely with XploreAsia, who is their in-country partner. They explain this on their website. XploreAsia is equally great, and once you get to Thailand, XploreAsia will run your unforgettable orientation week (baby elephants, Muay Thai classes, blessings by monks, Thai lessons, a beach party BBQ, meeting some of the most wonderful people ever!), find you a guaranteed placement (be open-minded, you probably won't end up on an island), and connect you with your agent. Your agent will be the person you'll go to if you have any difficulties at your school. If for some reason your agent can't resolve an issue, you would go to XploreAsia for help, and if you have issues with XploreAsia, Greenheart serves as a third party to help resolve those.
Greenheart also has a "Greenheart Teach in Thailand" Facebook page where past, current and potential teachers can ask questions, share experiences and feedback, and it's completely open and un-biased. Greenheart also links participant's personal blogs to their website. Reading these offers an extremely real glimpse into what moving and teaching in Thailand is like. I'd suggest taking a look at them and the Facebook page if you're seriously interested.
If you decide to teach in Thailand, I'd suggest leaving all expectations at home. When you arrive, you'll discover that people are friendly, but there's a big "mai pen rai" attitude, meaning go with the flow, don't let things bother/get to you. Thai people rarely get angry or show over-emotion.
Thailand isn't a cushy country, and no matter how great and organized your program is, you will encounter difficulties and frustrating situations. Sometimes they may be at your school (most of the time, it's because you're always told after the fact about what is going on - one day I arrived at my school and was told I was going on a field trip, which I only discovered the location of once we arrived), travel frustrations (mini-buses of doom without seat belts and hotels that don't exist), cultural frustrations, etc. And it's always hot. You will sweat a lot. If you don't do well with things not going your way all the time, then this might not be the country for you.
I'd also suggest being financially stable before you come to Thailand. Don't expect to pay off students loans or credit card bills with the money you make...you can expect to probably "break even" (cover your program fee and flights, cost of living, a little in-country travel), if you teach for one semester. There's a lot of costs associated with getting settled in Thailand (transportation to your placement, deposits on lodging, buying things for your apartment, visa runs after 3 months can be around $120, travel on the weekends, etc.) and it just makes for a much more enjoyable experience if you don't have debt looming over your head!
I have heard the visa process has become a bit more difficult because the Thai government is cracking down on Non-B visas, and recruiters are suggesting tourists visas (with a visa run every month until your school can get you a Non-B or a work permit), or education visas (which are costly). It's not really an improvement that can be made by the recruiter, but for potential participants, it's a good thing to research and be aware of.