Always note if it is a “pure” rally,
like “ONLY CAVALRY” – then send all cavalry you got!
Use your highest level commander as main + any commander with extra army size as secondary. The goal is to supply as many troops as possible to the rally.
Best is if you have a level 60 commander with leadership talent “Fresh recruits” and bonus army size skill.
Talent – Leadership “Fresh Recruit” gives 3% extra troop capacity!
Skills – Troop capacity:
Scipio Africanus (10%)
Julius Caesar (15%)
Mehmed II (10%)
Hannibal Barca (10%)
Sárka (10%) (This should be a last resort)
Examples with CH 25 (assuming max skills + 25% basic army expansion):
270k troops – Lohar level 60 + Scipio / Osman
296k troops – Scipio (Leadership) level 60 + Osman level 30
316k troops – Julius Cesar (Leadership) level 60 + Frederick level 30
March speed is the only other thing that can help, faster to the start of a rally, faster back home after the rally
The rally leader can kick people out of the rally while fighting, this way you can refresh your troops and re-join the rally!