A good first step to choosing the best flight attendant or air hostess courses is to research the career and all of its requirements. Also, the less expensive the courses, the better. Spending too much time and money on advance training isn't the best idea for one simple reason: formal training isn't required to get you hired as an air hostess or flight attendant. Most of your training will be done by the airlines themselves.
Despite the fact that they aren't required, taking air hostess courses is still a good stepping stone, and programs can be short or long. Looking at your other potential credentials might help you determine how many courses you should take, and what sort of investment to make. How much time and money you can spend will determine a lot, as will your confidence, people skills, and general intelligence. It's really up to you how much extra advance training you think it's worth enrolling in.
Although air hostess courses are not mandatory, competition means that they are still helpful. If you have a college education, a travel and tourism degree, or speak a foreign language, those credentials will make it easier to get hired. Airlines are looking for smart candidates that have good people skills and the ability to learn a lot of procedures. They are looking for candidates who are serious about their job, friendly, and highly competent. Specific air hostess courses won't help with those qualities, but they will show the airlines that you already have some of the training and that you're serious about this career move.
While a high school diploma is usually all you need to become a flight attendant, enormous competition for the work means that airlines can pick and choose who they want, and often they'll favor applicants with college degrees. If you don't have that, the more air hostess courses you can take the better, provided that you're sure you've got the other skills you'll need. It's useful to talk to flight attendants and the airlines to see what they are looking for in candidates. Having worked with people before, or in customer service, will also help your application.
In conclusion, choosing the best air hostess courses or getting an air hostess certification really depends on your own situation. Depending on the skills you already have, getting hired may very well hinge on developing some air hostess skills in advance, in which case, an exhaustive program could very well be ideal. The more you can learn the better, but keep in mind, there is no guarantee you'll be hired, and if you are, you'll still have to go through the approximately one-month training process, which you'll be required to pass, and which may include additional out-of-pocket expenses.