BMW R75 Motorcycle
This vehicle is great at hunting down snipers. But there is another great purpose for these vehicles in my book, for harassing engineers early game, just make sure you don't get to close, and if the engineer squad has the flamethrower upgrade, don't even bother. This vehicle is not meant to really be a support unit, however it can serve as a good distraction, flanking that Machine gun and drawing its attention as you have your volks squads rush forward. Just don't try to use this as a defence vehicle.
Schwimmwagen Type 166 
I guess it can be used with the same idea as the motorcycle, you know what, I'm gonna shoot straight with you. I have never used this vehicle. I always found the BMW R75 Motorcycle to be of more use, if any of you guys have any suggestions on how to use this vehicle, leave it in the comments down below. Sorry for not having more to offer on this vehicle.
Goliath
There's much to be said for this suicide bomber, if used correctly, it can be the enemy's worst nightmare, if used wrong, say goodbye to your goliath along with whatever other units you have standing nearby. Don't send this guy to blow up rangers, or airborne for that matter, they are just gonna blow it up before it gets there. In fact there are only two real times I would say use it. When you are attacking an enemy's base and you have a way to get it up to a building without it getting blown up, and when you have a decent chance of getting close to enemy's rear armor. There was this one game where I was playing with a friend on a bridge map, and we needed something to break the stalemate. So he built 10 goliaths and sent them all running at the enemy. It only took one shot from a antitank gun and boom, chain reaction. Destroying all his goliaths along with some infantry we had sitting to close, and all he could say was "oops." Don't do that, when you use these guys to break stalemates, send them in 1 at a time from different directions and you'll be fine.
dKfz 234 Armored Car
Alright, this guy can be one of your best friends as long as you get him out at certain times. Before the enemy has anti-tank guns on the field, and before there are loads of enemy tanks on the field. The way I use this vehicle is to keep it in reserve, revealing it when the enemy proves to strong for my infantry, and when I reveal it and they have to retreat ( and if there base is close enough) I follow them back to their base and finish off as many as I can. But I don't stick around long, I'm not a complete monster...sometimes. You should only get the upgrade "Puma 50mm Gun" if the enemy gets something out that you can't handle like 2 m8 armored cars and I desperately need something to counter them. This vehicle is weak when taking fire from anything antitank related, so be sure to let your infantry lead the way.
SdKfz 251 Half-track
Behold, the great halftrack. Capable of delivering troops to the front, and allowing you to reinforce on the field rather than having to retreat. This is one of the first vehicles I get up to the front, simply for the reason of not having to retreat my infantry when I need to reinforce. The "Flammenwerfer" upgrade on this vehicle is not really worth buying. But the "Walking Stuka," man that has broken so many stalemates I have found myself in. This vehicle however is very weak when taking fire from anything antitank related, so be sure to let your infantry lead the way.
Geschutzwagen
Whenever I use this vehicle, I use it on maps like hill 331, where I need to be able to get something antitank related up there quick. This vehicle is weak when under fire from anti tank guns/tanks/infantry with anti tank weapons, and should be kept in the rear while your infantry lead the way. This tank is as weak as a halftrack and should be treated as such, however it can deliver a knockout punch when it comes to fighting tanks.
Pak 38 50mm Anti-tank Gun 
Alright, this gun is beast vs tanks, especially when there's 2-3 of them, but you need to keep units close to defend them from infantry, preferably a volks squad with the mp40's upgrade. This vehicle should be kept near places where roads meet or choke points. Feel free to turn it invisible, but keep an eye on it as it will not open fire on enemy tanks when they come into view and must be made uninvisible before they will open fire.
StuG IV
This tank has better armor than a sherman. This tank is decently fast, but it's slow when turning, which basically means that a sherman can just keep driving in circles around you and you can't get a shot off. If you use this tank, use it as part of your attack force and keep it in the rear, only revealing it when you run into enemy vehicles and need a tank.
Panzer IV
Alright, this tank is more than a match when you run into enemy armor, but don't get cocky, unlike the sherman which can be upgraded to be able to fight infantry, this tank cannot. (At least not till you get all 3 veterancy on tanks which might be a while) I find that it's best to run these guys in groups of 2-3, that way when you run into those antitank guns or infantry, you have a better chance of surviving, not to mention that you stand a better chance in a tank battle.
Ostwind Flakpanzer
If there is one tank I'm okay with taking into battle against rangers and airborne, it's this one. It's ability to spam off shots that can kill an enemy squad within seconds is very valuable. However, I don't always choose to go for this, if I want something to fight infantry, I'll probably just get 2 MG's instead, but if the enemy player is doing a spam of snipers and rangers, that's when I'll bring out 2-3 of these. But yet again, don't have this tank lead the way of your attack force, have it in the rear but close enough up so it can shoot.
Panther
This tank is feared by many, including myself. When it enters the field of battle, I know it's on. This tank is best used in groups ranging from 2-4 and at full veterancy. Get that all together and you have an attack force all to itself, just don't rush them into into antitank units and you'll be fine. And remember this tank is more than a match for any tank the allies can produce.