If your dog is not reliable about coming, whether a formal "come," where he sits in front of you or just coming close or inside, I wouldn't use any cue yet. Only use a cue if he is coming. Treat him with a special treat EVERY time he comes to you and loads of praise. Later, when he's reliable, you can skip a few times with the treat. (every 2 times he comes, then every 4 times, then every time for a few, then every 5 times....skip around) When you bring him inside, continue playing something he loves to do. Don't stop the fun the minute he comes inside. Use treats that he loves while you're playing. Make coming inside just as grand as playing outside. (maybe not as wild)
You can go to him and put a leash on him to help him come inside. But, before you bring him in, after attaching the leash, turn him loose again. Repeat a few times. Let him know that putting the leash on is not the end of the fun. Give him a treat and lots of praise each time you put the leash on.
The important thing is to NOT use the word, "come" or any cue word unless he's already obviously coming. You'll poison the cue if you use it and he doesn't comply. He's not being stubborn if he doesn't comply. Humans need to be careful not to attribute the degree of logic that we have to dogs. They don't test you or blow you off. They're not that complex. He's just doing what works the best for him, being an opportunistic animal. If something outside is better than coming, he'll keep doing what's more motivating. So, you have to become more motivating. And coming inside has to be a really cool thing. Dogs aren't like people in that they "know" better but choose to disobey. They just plain do what works for them. That's as far as it goes in their brains. That's why we have to train them.