Favorite is really the wrong word. What I actually mean is the main indicator; the one that would trigger the trade (unlike indicators used for confirmation of entry/exit) or the one that will confirm a trade based on price chart formation only.
I like many of the indicators such as the ADX and the Stochastic; however, when determining the trend of given market I primarely rely on the 2P V4 Trend Indicator, which is part of the 2P Trend Indicators by http://www.2pinvestments.com.