I'd say open guard. There are some things that typically cause anxiety for new people. Being crushed under heavy pressure, claustrophobia, fear of getting your guard passed, fear of "losing," and just not knowing what to do.
To avoid these things, new guys will often lock down. They'll either desperately avoid losing top position or they close their guard and hold on for dear life. Ultimately, these are self defeating.
Starting with an open guard will lead to good defense, as you WILL get passed often. You'll develop solid survival skills from bad positions, because you'll end up in bad positions often when people pass your guard.
You'll also quickly get over any fear of losing, cause this concept really doesn't exist in training. You're either getting better or you're not, and you're not getting better if you're not struggling out of tight spaces.
Opening up your game will free you mentally to go for submissions. If you're not afraid of losing position, you'll go for that armbar, triangle or omoplata. Once again, guys who are afraid of losing position will lock down and hold on instead of opening up their guard and working for a sweep or submission.
So, open guard. That's my suggestion.
