For example for a pick 6/45 or pick 6/41 which method do you think is the best
to play with only a few numbers ?
You have to take a number of factors into consideration such as jackpot and lower tier prizes and select the game with a little edge in your favor based on your style of game play.
For example, if you want to play a cheap 3if6 (16,6,3,6)=5 wheel the game needs to pay a prize for 3 numbers correct.
If there is no 3if6 prize, walk around it and play a cheap 4if6 wheel (12,6,4,6)=6.
In general the smallest game with a prize(s) worth winning is the way to go.