Choosing a driving instructor is a tricky business. Learning to drive involves being in an enclosed space with someone you don't know for hours over a period of months. In an ideal world, everybody would be recommended a good instructor who was knowledgeable, patient and respectful. Unfortunately this is not an ideal world and while many people get on fine with their instructors and pass quite happily, others have terrible stories of bad instructors and take years to get through their test.
If you are learning for the first time, I would not recommend intensive courses. These are useful in certain circumstances, for example if you learned to drive a while ago but did not get round to passing your test and just want to refresh your memory and get it done then an intensive course would be fine. However, driving is a complex skill and it takes a while for all the things you are learning to sink in. It is always amazing to see how much people learn when they are asleep or doing other things between lessons! Learning for the first time you are much better off having regular lessons with a good instructor.
Choosing an instructor is difficult. Most people are recommended one who taught a friend or the older sibling of a friend. This is a good way to find one as you have the evidence of their success already as well as a referee as to their character. If you don't have a recommendation then there are a few things to consider.
Potential driving instructors can start to teach before they have qualified on a temporary licence and some of the big national and local schools employ a lot of trainees because they are making money from training them too. This is not always a bad thing as some new instructors are very good and many who have been in the job for years have not updated their knowledge and skills but it is worth bearing in mind. However, large firms have the advantage of a choice of instructors so if you don't get on with one, you can just ring up and ask to try out another.
Local firms with more than one instructor are obviously successful otherwise they would not have had to employ a second one. Driving instructors are nearly always self-employed (only the very large firms actually employ instructors, most pay a franchise) so if they are busy then they are probably good.
A very important thing to remember is that if you don't get on with your instructor, you don't have to stick with them! Unless you live in a very small place with only one instructor for miles around, there will be a choice. Even if everyone you know got on fine with your instructor and passed first time, if you don't like him/her, or you don't seem to be learning anything, you don't have to stick with them. We don't all like the same people, sometimes it just doesn't work. That is ok. Learning to drive is stressful enough without being stuck with someone you don't get on with!