In terms of your team it doesn't really matter what squads you bring, just make sure you keep the following in mind:

1.You need at least one melee tank character to take the aggro and keep the enemies all clumped up on the spawn point

2. With the other three it's best to build as much DPS as you can have on them. Also keep in mind that AoE or high fire rate damage is better since most of the enemies are squads, with a handful of solo targets. The faster you kill the enemies the faster more will spawn and the faster you will complete the mission.

3. In terms of consumables, turrets are pretty essential, healing is always good, and remember that you won't be going out of your way to get the ammo boxes, so do you really want to bring those grenades?

There are a few things you want to do as soon as you spawn in. If any of your squads are using refillable items you want to break open all the spawn crates and pick up 2 of the drops, since most items only spawn you in with 3 of 5. Then you want to start setting up your turrets and mines. You want to try to put you turrets on each direction the enemy can come from and then drop the mines closer to the generators. If you are facing against Eldar it is much more important to have you turrets closer to your generators so they can guard them against the teleporting squad they have.
Here are a couple example setups, turrets in red and mines in blue.





The first of the above setups is against Tyranids, while the second one is against Eldar. As you can tell the Eldar Turrets are much closer to the generators...



...to stop those guys

If you didn't already know, each wave of enemies in defense missions will spawn at a single point, even if you are right next to it. This makes it easy to just set up on the spawn point and clear the wave as fast as the spawn timer allows. As soon as the red arrow pops up showing you which way the enemies are spawning from, move all your squads towards it. Once you are in sight range of the spawn point the arrow will disapear. Get you tank right on top of the spawn to instantly aggro the spawning enemies to stop them from moving and open up on them with you AoE and DPS abilities. Here are a few screenshots of the spawns taking place, the first and second images are only seperated by a second or two.

Take a look at this screenshot:



There are a few things you should notice:

1. The first enemies of each wave actually spawn and start coming towards the generators before the wave officially starts.

2. I have already started moving my squads from the last spawn even before I knew where the new one is. It is possible for the next wave to be in almost the same place, but why risk losing precious time.

As soon as you finish a wave, move all your squads back towards your base, and as soon as you see the red arrow showing the next spawn location, move towards it. On some of the maps the enemies may get to your base first, but that's why you dropped those turrets earlier. The first wave will stop to attack the turret in their way and buy you a few seconds to get there and mow their conviently clumped up bodies down.

Using this method I haven't finished a defense mission in over 6 minutes. So if you follow this guide you should have no problem getting all 5 speed medals every single time. Your fury medals may vary as sometimes it takes into account the randomly spawning enemies on the map but I find you won't get less than three of those and depending on the amount of foundries you have 13 medals is usually enough to get your extra 2 deployments.