How many numbers are optimum per spin?

[albalaha]

One of the most considerable debate on roulette:

            How many numbers to bet upon per spin? In my opinion, it could be anything from Six to Nine. If we select Six numbers, it could be a pie or star of the wheel as defined by Kimo Li or  a Line bet or maybe something else. If we have to take Nine numbers, one can bet upon a quarter of the wheel which is hot that time or all numbers that are black as well as odd; or red as well as low etc.
                      There might be different players around which can say outside bets (EC bets and 2 to 1 bets) are best choices but here I am talking about inside bets only.
                  Please provide your reasons for your favorite bet selection, so that we can learn from each other.

[Fripper]

In my new studies I like to look at 1-15 numbers. I don't want to go beyond 15 numbers, 15 is my limit. Sometimes I go from just 2 or 3 numbers and then up, or I start with 6+ number for example, it differs alot.