TheMeinTeam:
I like doing MT occasoinally from Lib, but you need Nationalism for that, and getting or trading for Nationalism before MT isn't as easy as getting Chemistry, for some reason.
My usual scenario in beelining MT is to use Lib to get Nationalism, then tech MT manually (or with Great Artist help).
I've been forced to self-research it lately (probably means I should move up to immortal full-time, but I'm enjoying emp blowouts for now

). However, the AI does seem to like it. Sometimes they'll get it before education, which is pretty nice.
The hard thing about chemistry is its engineering pre-req. I like bulbing down liberalism path, so the typical situation looks like:
I have lib. I only have metal casting, not machinery. I want to attack someone (don't I always?!), and I want to use a renaissance unit ASAP.
To get chemistry, I'd have to trade for machinery engineering, then either bulb it (assuming I have PP, not likely) or trade for that too, all before lib!
It's often doable to get steel anyway. Especially if you are doing well enough that you're trading philo + a small tech for machinery or something (or CS even better), and the AIs aren't set to win Lib, you can often self research chem and take steel with lib. I can't envision too many scenarios where that's actually EASIER or FASTER than MT, but that doesn't mean MT is better. Cannon can do collateral and have the nice double-usefulness of bombardment too (cuirassers need spies typically, or low defense perimeter cities).
The bigger the target, the more I'd lean toward rifles or cannon...but usually big targets don't sit around and wait!