Building the War Machine

Throughout the StarCraft II: Wings of Liberty single-player campaign, players embark on new missions and unlock additional units. A vast array of challenges awaits Raynor’s Raiders in the Koprulu Sector and Rory Swann -- chief engineer of the Hyperion Armory -- works tirelessly to arm the troops with the tools they need to put the hurt on Dominion, zerg, and protoss forces.
As you delve further into the campaign, you’ll notice that the choices for air, ground, and vehicle support become extensive. In fact, you’re often presented with several options for the kind of offensive campaign you want to wage, with just as many choices for setting up base defenses. We want to know: what air, ground, and vehicle units do you gravitate toward because they simply rule?
You can find a list of the multiplayer units here. Don’t forget to consider the additional units you have access to in the campaign!

In personal Opinion, nothing can beat this classic combo: Firebats, Marines, Firebats, medics, and MORE Firebats.
Actually thinking about it now I really didn't have to much in the way of specialization. Generally I always wanted a balanced force, so goliath + medics + marines were usually the brunt of it, but I also went BC victory fleet, mass vikings + shees for an air level or two (tech reactor=teh awesomes), mass tanks and goliaths for the defense levels, a few ravens ect.
So pretty much all over the map.
http://www.teamliquid.net/forum/viewmessage.php?topic_id=140954
Terren:
I loved the Firebats to start because I was fighting mostly zerg ground units and you couldn't bet there AOE damage, but it was the Medics that made the biggest differnce in my infantry I would place 2 behind my six man bunker (2 marines and 2 Marauders) and an engineer (auto repair is AWSOME!) this was my very affective basic defense most of the game increase to 3 bunkers in at triangle (the back bunker all marines) at entry ways by the end of the game and adding 3 siege tanks and 3 anti air turrets.
I loved the diamondbacks as my favorite vehicle for assault, because they could rip through a base and stay moving which allow low losses if controlled well, but as soon as I started getting serious air to ground resistance only the Goliaths would do. The Thors ended being more line holders due to there size and vulnerability to air I would place them at the front door and fly my goliaths just past the man defense to there production buildings.
Vikings were the only air that mattered, to me. Don’t get me wrong I love the battle cruiser but the fight is usually about over buy the time you have a good armada going and Vikings hold there own in the sky even if they have to be dropped carefully to make them useful on the ground they make good support to goliaths they can clear the air turrets then redeploy to the sky to fend off the more troublesome air to ground assault units like void rays, carriers, Brood lords.
Protoss
I love the stalkers and void rays! A hand full of dark templar and a couple of observers, you blink in hit back end detectors and blink to the front where your void rays eat are eating the front of the base then send in the observers and dark templar targeting air construction/detector buildings being built, then workers and clean up. They other units are all defense as far as I am conserned.
As for new units I am loving marauders, and Thor. I wish there was an expanded skirmish or custam map option that let me play my campaign units (with chosen relic upgrads, and purchased tech) in a variety of map modes.
I love my f-bats, I always am sad to leave them behind when I'm not in campaign mode. :(
Tell me it's not fun having Marines, supported by Medics and Marauders reinforce a Firebat and Reaper rush with Ghosts moving in for multiple Nukes.
& stalkers r my best protoss
An infantry group I run around with are some marines, some marauders, and some medics to just blast through everything. I'll have 3 full (3 X 24) groups of those units together.
I also like to keep some spectres (spelling?) on the side to nuke a heavy force, or sneak in. The ghost of a chance and the other mission with Tosh were my favorites. Sneaking in and destroying everything.
I do wish that in the future when all of the 3 parts of Starcraft 2 are released that Blizzard makes a function similar to the talent tree in WoW which lets you customize your units like in campaign mode. I'd rather use spectres instead of ghosts, and I like bunkers with a carrying capacity of 6. I think Blizzard should work on balancing some "talent" trees to customize your own forces to play in a multiplayer setting.
Of course, the customization seems reasonable only after all of the 3 parts are out so the Protoss and Zerg players are included.
TLDR: I like
1. mercenary battle ship
2. marines with marauders and medics
3. spectres on the side
4. customizing my own forces
I wish to customize my forces for multiplayer
Actually, having seen Goliaths in action during the campaign I really wish they were in skirmish, terran AA doesn't happen till vikings, and they're not the answer to everything....