Speaking only about what is, imo, most advantageous,
You should never not pick Mobility because you don't have the 'correct' tech teams.
1. You can always keep more up-to-date by sacrificing other techs - researching earlier + researching for longer.
2. You probably have a team that is not that bad at it... IIRC, matching a single research slot reduces research times by 10% on average.
3. If you have a decent tech team (6+), you can keep up-to-date with Mobility tech even if the tech team doesn't match any tech research slots.
Mobility is just so much better than anything else that even if you're lagging behind in tech, your units are probably well-ahead in performance.
With that in mind, if you have a wonderful Firepower tech team, Firepower is certainly not a bad choice, and IMO the closest to Mobility mid-game and later on (based on event chances, HQ modifiers, GDE, bonuses, etc.) If you are concerned with roleplay/cheating/gameyness, I'd pick Firepower over Mobility for Italy.