There is no 'perfect' job. There are very good jobs, but familiarity usually breeds some contempt. I'd always advise any teacher to avoid working for an agency. Really, the best compliment I've heard about any agency is "Well, they always pay on time". The bar is clearly set too low.
I worked for two schools through two different agencies. Both schools were great, but the agencies were always a pain. Anytime anyone from the agency came to the school it put the foreign teachers on edge. Often it made people nervous because the agency were too overbearing about looking and behaving perfectly. They were obsessed with looking good and keeping their contract. That's fine, but have some faith in your teachers. You employed them after all. Both agencies paid on the right day, but you'd never know what time. It was never before lunch and one time it was at 9 o'clock at night. There's only really one thing I expected from my agency, pay the money on the day and preferably in the morning. You have one job.
Now I work directly for a school and it is awesome. I have a boss who studied in the US so I can talk directly to her. There's no middle man diluting or simply not passing on information. She's a businesswoman first, but she's smart. She sent me on a course to learn how to use and utilize my interactive whiteboard. I have a projector, laptop, printer and awesome wifi. I even have a pleather office chair. I got an extra 5k for summer camp and a 'thank you' because we had a lot of students signing up. That really made me happy. Even just a thank you sometimes makes a huge difference. It does to me. People need to feel the love sometimes.
It must be tougher for agencies now to find teachers. Salaries are still rubbish and places like Bangkok are becoming more expensive. I know one young guy on 35k who recently quit. He said the money wasn't enough and he didn't come to Thailand to work two jobs. He's going back home. Thailand is an amazing place to live, but nowhere is fun to live if you don't have enough money. Me working directly for the school has netted me an extra 15k a month. I wish it had happened sooner, but I think I've earned it now.