to be honest, just get one that fits you best, i wouldn't buy a 105 equipped frame if it's one size too big/small(be-careful the lbs guy trying to unload left over even knowing it's not a
perfect fit for you)

we can argue all day about material selection, groupo difference and frame geometry and you'll will not be a better cyclist.

just get something that fits you well and start riding til it breaks, don't upgrade to ultegra just because someone over the internet told you to, after a few thousand miles you will
reach a point that you know what you want to upgrade. if you started out on a right sized frame, you shouldn't have much trouble fine tuning your component as you get more advance

edit: sora/tiagra are perfectly fine for beginner, try them both to see if it's worth the upgrade.