I often see people talking about how they find Medium battle difficulty too easy, and thus go for the harder levels. But what I never see is any mention of what armies they're recruiting, and how they're using them.

I half-suspect that the people who say that recruit stacks composed almost entirely of principes for their infantry, accensi for skirmishers and the odd few triarii and cavalry. Or perhaps a group of family members for their cavalry. Based entirely on effectiveness, rather than versimilitude.

Mine is as close as I can get to a proper consular army in one stack. As detailed in my guide, thus:

Camillian
The Roman core of a Camillian consular army is two legions, represented by the following units:
1 unit of Leves
1 unit of Accensi
1 unit of Rorarii
2 units of Hastati
2 units of Principes
1 unit of Triarii
1 unit of Equites

The two socii alae are composed as follows:
2 units of allied skirmishers (any mix of javelineers, archers and slingers)
4 units of allied infantry (two different pairs of Samnite, Lucanian, Bruttium, Ligurian or Gallic infantry, or pedites extraordinarii)
1 unit of classical hoplites
1 or 2 units of allied cavalry (Campanian, Greek, Gallic, Ligurian or anything else available, or possibly equites extraordinarii)

Polybian
The Roman core of a Polybian consular army is two legions, represented by the following units:
1 unit of Velites
1 unit of Accensi
2 units of Hastati
2 units of Principes
1 unit of Triarii (or two if you're playing with half-sized maniples)
1 unit of Equites

The two socii alae are composed as follows:
2 units of allied skirmishers (any mix of javelineers, archers and slingers)
4 units of allied infantry (two different pairs of Samnite, Lucanian, Bruttium, Ligurian, Gallic, or Iberian infantry, or pedites extraordinarii)
1 or 2 units of allied cavalry (Campanian, Greek, Gallic, Ligurian or anything else available, or possibly equites extraordinarii)

Marian
The Roman core of a Marian army is as follows:
1st Legion
1 General
1 unit of First Cohort
1 unit of cohors reformata
1 unit of antesignani

2nd Legion
1 tribune
1 unit of First Cohort
1 unit of cohors reformata
1 unit of cohors evocata

Support
1 unit of Scorpions/arrow throwers

The allied part is as follows:
1 unit of allied javelin-men
1 unit of allied slingers or archers
1 unit of allied cavalry
Optional: 2 units of allied close-order foot

This represents two legions and their supporting artillery, light troops, cavalry and allied infantry. Feel free to add additional support units. A third legion can be presented by adding three more cohorts as above.

An option for early post-Marian troops is to have just the First Cohort and two normal cohorts as one legion, since there were as yet no veterans to draw upon.

Disposition
Camillian and Polybian armies should be deployed in the triplex acies, three lines giving strength in depth and keeping most of your forces in reserve. Marian forces can be deployed in three, two or even one line as befits the situation.

Key:
Gen - The general
FM - Family member
Tri - Triarii (or allied hoplites)
Pri - Principes
Has - Hastati
Ski - Accensi/Leves/Velites
Ror - Roraii
ASk - Allied Skirmisher
ALI - Allied Light Infantry
AHI - Allied Heavy Infantry
Cav - Cavalry

Camillian and Polybian

----ASk----Ski----Ski----ASk
Cav-----ALI----Has----Has----ALI----FM/Cav
----AHI-----Pri-----Pri-----AHI
--------Ror-----Tri-----Tri-----Gen

Placement of the General varies, as long as he's behind the fighting line it doesn't really matter. The only difference between Camillian and Polybian armies is the absence of the Rorarii.
Thus my hastati and the allied light infantry get chewed up holding the line in every battle, while my second line tends to take quite light casualties.

What about you? Do you have a "standard army"? Do you use a standard deployment of some description?