Warhammer is a game of Wysiwyg, or what you see is what you get. After being inspired by Ron from From The Warp, I took a look at what I played and how. I like theme armies, I freely admit it. I will play an all terminator Deathwing army with Belial, or, on the other extreme, an all assault squad Blood Angels army with commander Dante. I will play an all scouts Space Marine army. I will play a Nidzilla (Tyranid Monstrous Creature list) army. Will I play a balanced, effective, well thought out army. Not so much.
Perhaps that is why my main opponent is my five year old daughter. She usually plays Orks. They are a good old fashioned 'charge straight at 'em and chop 'em up' type of army, and I again freely admit that she usually beats my theme army du-jour. Doesn't stop me, however, because I have more fun with playing the theme army than I actually get from winning. Plus, her winning keeps her in the mood to play more!
My current thing is 'counts as.' I love the Tau models. They look like what sci-fi should be to me. Maybe that's what I get for growing up watching robotech with my brother. Also, as much as I like the gothic medieval freakshow that is the Imperium of Man, sometimes the no psyker, no religion aspect of the Tau is a breath of fresh air. They have guns, they wear armor, they are not good in hand to hand combat. Aaaah.
On the other hand, they don't have commanders that give them special troop selection options. This leaves me in a bit of a quandary as it pertains to playing my favorite models. I can either play with kenchan's Super Simple Rules (which is the usual answer, and is easier for my daughter anyway), or come up with something on my own. I can squadbash my way into Death Squads, meaning 'umm, yeah, that XV25 is really an Imperial Guard Leiutenant in carapace armor with a shotgun'.
Alternatively, I can be a little creative with the army lists, and pick another army commander and list to make the models I want to have happen. So, XV-25s, A Crisis Suit, and a few gun drones, but not with their own rules, played instead as...I dunno Dark Angels Deathwings, or Blood Angel Assault Squads. Maybe there are other theme lists from the other codexes that I don't know about. Any ideas?