Most of what I'd contribute has already been stated eloquently by a few, and I do love/own bricks of Monarchs.
However, if your goal is to be the best mechanic you can be, and do what a mechanic does best, I can tell you that you would be doing a disservice to yourself by not trying and USING many different decks in all sorts of shape to achieve that goal.
A solid mechanic needs to be able to function with ANY deck, regardless of finish, brand, or condition. A mechanic and a magician are two very different animals with some crossover.
That said, after years of working on my craft and spending exorbanent amounts of money on bricks of T11 and E decks, Tallys, aviators, bees and bikes (of which I like all for various reasons), you should seriously consider looking into some Turner Gold Seal Bikes, as well as some 809 Mandolin Bikes. The prices on both are ridiculously low for the quality you get. Look em up, you won't be disappointed.
Good luck, work hard, and remember along with working with new fresh decks to pull out your old decks of all conditions and work them as well. It's probably the best advice on mechanics I can offer.