Technically, the most productive and effective location are extending the Central Incisors. Albeit effective, it looks rather dorky (think Bunnicula) and can't carry much force, but is best for strictly feeding with little damage to the target. The Lateral Incisors are a little less effective, a bit better looking, and have a touch more force behind them, but often lead to the fangs ending up extending out atop the lower lip when the mouth is closed. They're best when going for a dramatic fear-factor style attack. The Cuspids are the ones most commonly extended. They aren't as feeding-effective, but allow for easier speaking and can carry a fair degree of force. The First Bicuspids carry a slew of force (if you're trying to crack nuts with your teeth, you generally tuck them back behind the Bicuspids), are easy to conceal, but require greatly extending the mouth in order to do any feeding. If a vampire is using a bite as an attack and not for feeding (doing Str+1 Damage), it's not unheard of for them to muckle on with a large bite and then extend the First Bicuspids. Due to the intrinsic structure of the human mouth with a natural overbite, extending the lower teeth into fangs are only done for intimidation or post-bite attacks.
Early on, a vampire will generally settle into the tooth-option that suits their purposes best and that they happen to like. Nosferatu, Tzimisce, and others that don't care about appearances tend to go more with the Incisors, but Ventrue, Toreadors, and others that try to get points for style tend to more go with the Cuspids. Due to their Banality, as the years pass, an Elder vampire will tend to settle into a pattern instead of going with the more efficient option.
When I think 'house rules', this is what first comes to mind. The sorts of things that one would figure out in the first few days of being more (or less, depending on your point of view) than human.