Don‘t underestimate wheels! 2vs1 they will heavily damage ANY infantry, even zones/cyborgs. Their fast speed also enables them to reposition very quickly. When mixed with lasers they become even more dangerous since the enemy now has to clear infantry (lasers) and vehicles (wheels) off of the field. If you would use militants, fighting no vehicles makes it easier for your opponent to counter. Having both militants and wheels in your deck is actually effective, since wheels can attack units which are dangerous to the militants, but not the wheels. Unlike the militants&chembuggy combo, wheels only cost 10. I get to tib league very often by just going no harv and only building wheels and lasers. With good micro, even only these 2 units are dangerous. Adding fanatics and bikes makes for a good no harv deck.
Dogs don‘t have that much dps, but what they do have is tons of HP. Blocking with them is very effective. I usually position dogs in front of my snipers so they can take out beefier infantry like chemtroops. Stealing pads also works great. Unlike wheels, dogs usually make it to the pads without getting completely destroyed. Another good thing is that talons/venoms don‘t do anything to dogs. Riflemen just die to those way too quickly. Tried using snipers with riflemen... I just hate it. Shockwave spam kills em both.
Conclusion:
Nod: You can use militants or wheels, it depends on what you like more. Using both in the deck works too. I personally prefer wheels, but I often use militants too.
GDI: Rifles are for damage, dogs are for protecting pads and your other units. Here you can‘t just pick the unit you like more, you need to make sure the unit fits in with the rest of your deck. I personally use militants only when I don‘t have snipers/shocks in my deck. And since snipers have very high dps and range, I use snipers, therefore I also have dogs in the deck.