Given what you said about your current situation, I'd say Mont all the way.
-Mont is easier to train on the side if resources are tight;
-Mont can better protect Mediena in PvP given his superior movement to Engel;
-Mont isn't as tanky as Engel, but he can get the job done in his own right;
-Mont can easily handle Cids and Freds, just stay away from Lu'Cias and Yermas in PvP.
And there are dark units that are capable of one-shotting Engel. There are ever evlolving strategies to counter any unit in this game much like others. Advice doesnt become bad because you can think of a single unit to counter someone else's logic.
You talk like someone who's never used 120 EX Mont and are just judging him off the fact that he's a free MR unit. Use him first before you bash him. 120 EX Mont is better than 99 Engelbert and slight worse than 120 EX Engelbert. Considering it takes significantly less time/resources to build Mont, he's definitely a good choice for new players.
herrr durrr he get's one shot by lucia,
Gee smart@ss its almost like he's weak to wind you dipsh1t. Engel gets his sh1t kicked in my my duane, KoR, or 120 Sterne.
There's elements for a reason you r3tard.