HTP or MoN for Mechanic?

MoN is better for some classes because of the 10 attack an average MoN adds. Some classes get more out of weapon attack than others because of their skills having high % damage rates. HTPs are good for other classes that could benefit more from having +23 to their primary and secondary stats (I believe that mages were the only ones that fit this category, but that was pre-BB), or if they require the extra stat bonus to equip a weapon that would give more than a 9-12 attack increase. Also, I don't think MoNs can ever be given potential, which means that a HTP with potential can become better than a MoN even if you're of a class that benefits more from attack.

Now, as for which one you want, I'd say you might want a MoN since mechs have enormous damage percentages from their skills, but as ,Shidoshi has already stated, you'll be better off with a HTP if you can afford one with good potential stats.