posted February 13, 2013 08:50 PM
More often than not, Libra and Capricorn Mercuries (IME)~ with Scorpio and Pisces Mercury being invaluable often times as well -My guess is for Libra or Capricorn though~
It's not so much the house it's in that would contribute to the person as the houses it rules, and what is sitting on their 3h, 6h, (possibly 7-9-11h) cusps, and the interactions between those rulers and Mercury itself, in its house.
Sagittarius and Libra rule matters of good judgement/law. (Mercury is weak in Sagittarius but, that only accounts for one placement, and the aspects within the rest of the chart would have to be heard too, right?!)
Leo, Capricorn, Pisces, and Scorpios are known for their keen perceptions, and being good at speaking out/recognizing truth, handling complicated matters, and that could lend itself to giving "good advice".
Virgo and Gemini are ruled by Mercury and natural rulers over the 3rd and 6th houses, gift of the gab isn't always the best for advice, though they may like the sound of their own voices...^^ so, you will tend to easily come by their opinions... I'm not sure if that is always going to be valuable. XD
Mercury in aspect to Jupiter, Venus, and Saturn will lend itself to being mindful, and diplomatic... in their own ways, of course.
something like a Virgo rising with Mercury in Libra 1h~
that person, would undoubtedly have a good strong opinion... ~
just my thinking though~ ^^;