Optimus Prime:
OP isn't too big on affection, especially in public. So his hugs are more subtle. An arm around your waist or a quick hug with a kiss to your forehelm.
Bumblebee:
He loves you. He love, love, loves you soooooo much. He smothers you in full on bear hugs almost every day. He's just that adorable.
Smokescreen:
Smokescreen doesn't get all "hot and steamy" per se. But he always found a way to hold you, hug you with his servos running up and down your back.
Megatron:
The leader of the Decepticons almost never showed any affection among others. The most he would do was probably place a servo on your shoulder to acknowledge your success. However, he made up for it once you two were alone.
Soundwave:
Ah, the silent one. Who says he can't hug? If it's not with his own arms then he's most definitely using those extra appendages to slip around your waist and pull you to him.
Knockout:
The Doc knows what's his. And he makes sure everyone else knows it too. He likes to wrap an arm around your waist and keep you close. Sometimes his servos might be a little too close to your aft. But he always denies doing it on purpose.