SOVIET
Soviet's are a good too, if you like the powerful type. With Heavy tanks, and Mammoth tanks, they pack a large punch. I think the best part of this side would have to be the Mammoths, Tesla Coils, and MIG Airplane's. Mammoths may be slow, but they can attack infantry, air units, and any type of ground unit. The advantage to Tesla Coil is it's long range, and VERY POWERFUL. The MIGs are excellent when they attack in packs. I would not recommend using YAK airplane's. MIGs are fast, launch rockets, and can take out a construction yard if you have about 10 of them. The thing you have to worry about with airplane's is the Anti-Aircraft Guns (AA Guns for Allied), and SAM Sites (Surface to Air Missile for Soviet) Without the Aftermath add on, I wouldn't recommend using the submarines. They're slow, they only launch torpedo's, and the only good thing about them is they're invisible when underwater.
Below I have listed, in order, what you should build to have a good Soviet base:
Power Plant Advanced Power Plant Barracks (build grenadiers) Ore Refinery War Factory (make heavy tanks) Radar Dome Ore Refinery Soviet Tech Center Tesla Coils (enough to surround your base from all possible entries) Flame Towers (some around your construction yard) Repair Depot Ore Refinery Sub Pin (if you know that you're opponent(s) have build one as well) Whatever you deem strategic
Somewhere around building the Sub Pin, it might be a good idea to build some airfields, (this is only if you have extra money.) This way, you can have about 10 MIGs, and be ready for and attack. MIGs are fast loading, fast shooting, powerful airplanes that can easily take out a construction site in one blow, (if they're in packs.)
TIP:
To maintain a good base, you should always have at least 5 MIGs ready and loaded, and enough Tesla Coils to surround your base. For each Tesla Coil, you should have at least one SAM Site, and maybe more. I would suggest building 5 or 6 Ore Refinery's, depending on the size of your base. That way, you can build what you need to build (Tesla Coil's, Mammoth Tanks, Infantry), and still have some money left over. I especially like the maps with the large amounts of ore. Also, if you bookmark their Tech Center (like the tip above), and you know your A-bomb is almost ready, you can begin building up massive amounts of MIGs, and Large/Mammoth Tanks. This way, you can do a full frontal attack. Of course it helps if you're fairly close to your opponent, since the tanks are so slow. If they get another Tech Center up, and send some scouts out, they'll see it coming, and be able to set their defenses up.