Or let me put it this way... do you feel more earthy, or more airy?
Earth would be "down to earth"... simple, basic pleasures of life...
Air would be intellectual (of course with Mercury you already would be) but also detached, abstract... less concerned with physical pleasures. More concerned with thinking & keeping yourself busy in the mind.
Do you see where the difference comes in?
Mercury in Taurus on the Ascendant might make you talkative or a thinker, or move around a lot, but you will still be concerned with having your basic 5 senses met (like a Taurus would). You would still be "down to earth", quite simple really, or basic, in your needs, requiring wholesome or practical, good quality & stability over flimsy or changeable. You would just be more mental with all of these things.
If you were Gemini Ascendant, you would not be concerned with the 5 senses (like a Taurus is) and would be less physically oriented, and really pretty much being an intellectual thinker, living in your mind, always thinking things through, remaining quite detached, and preferring changeability, versatility, and socialbility, charm, sarcasm... really without caring so much at all about the "earthy sensations" or pleasures that a Taurus Ascendant cares so deeply about. Taurus is all about having their 5 senses covered! And cautious, practical, and stable! That's it! Slow to anger, but when they do, they can explode and not give up. They are also very attached to things. Resistant to change. Even with Mercury on this influence, I still think the Gemini will be easy to tell because it would have none of these Taurean traits. If you are Taurus ASC, like I say you will just be a more talkative & mental Taurean, but still preferring earthy sensations, and needing them to be met or else you will not be comfortable at all. These earthy "needs" are absolutely essential to the Taurus ASC.
P.S. Also think about the Descendant- In a marriage partner, do you look for a SEXY, deep, intense, emotional, loyal or powerful partner? (Scorpio- opposite Taurus Ascendant) Or do you look for a foreign, different, philosophical, religious, well-learned, traveling, cultured, truth-seeking partner? Honest and natural, blunt/outspoken or probably hard to pin down or to get to commit? A searcher? Seeker? Freedom lover? Independent? Maybe even a teacher? Somebody wise? Or a clownish type personality? Funny and outgoing? Life of the party? Social? High goals and aspirations? Larger than life? Lucky? That would be Sagittarius (opposite Gemini Ascendant). See if any of this resonates with you... I would think one of these seems more like what you would be magnetically looking to complete the other half of you. For me, with Taurus Ascendant, I am magnetically attracted to a deep, loyal, sexy, intense or powerful partner. I'm sure you will be able to see the difference in these two and hopefully one of them pops out to you as the one which seems right.
--And I mean not just "attracted" to... but which one you really NEED. In order to feel safe and secure (Taurus/Scorpio) or entertained and informed (Sagittarius/Gemini). Is security & loyalty what you NEED in marriage, or are you more of a versatile, less attached type of person? More concerned with fun and knowledge? (Sag/Gemini...) When it comes down to the nitty gritty's, are you more concerned with making sure your partner doesn't cheat on you? And that he stays deeply loyal, loving & committed to only you? Or that he is entertaining and fun & knowledgeable? Not worrying about that kind of stuff, allowing him freedom and personal space? Not minding so much if he travels or spontaneously does his own thing away from you? There are major differences. A Taurus ASC woman wants to be able to count on her partner. Wants him home to keep her safe at night and know that he is loyal and true to her. Much more focused on security, loyalty, and those types of basics in a relationship. Wants somebody to depend on who won't just up and leave her some day or hurt or betray her, or not stay true to their word.