Hmmmm that's an interesting question. In my opinion the strength of the non-noble line of Sarleon troops lies with their Halberdiers. They are very good against cav of course, but also - and this is something some people seem to misunderstand - they are just as good vs infantry. In fact they are fantastic vs infantry and can chop through even the most heavily armored formations. They deal massive damage and have the added benefit of being able to strike from the back rows of a formation, whereas with other types of inf only the front row can fight. If you use formations a lot this is a pretty big deal.
But of course the draw back is that they lack shields, and they take forever to train, thus on an open-field battle archers can deal some serious pain on your army (especially if you have no cav), so you definitely need man at arms for their shields.
The Armored longbowmen never really impressed me to be honest. I mean, they are OK I guess, but they are not that good, and are in my experience easily outmatched by any faction with decent archery power (i.e. Armored crossbowmen, Ravernstern Rangers, Veccavians, Barclay, Noldor, etc.). So I'd say just ditch them, and go full inf.
So my army choice would be something like 40% man at arms and 60% halberdiers. Put them into shield wall formation - that way the halberdiers are in the back rows protected from arrows - and march them into battle. This is for field battle purposes. If you are planning on sieging a lot maybe have 15% longbowmen just to distract and take out a few of their archers, although don't expect much from them. If this is a garrison force - as kevinflemming said - you need a substantial archer force.
It is important to add that your army comp can be altered to match who you are facing. For example if you expecting to fight the Fierdsvain - whose archers are awful - having a majority force of longbowmen can be a great idea - especially in sieges. But vs most other factions I'd go with a majority inf and maybe a token archer force (or non at all).