Great questions, as these are three very equally matched "smaller" naked bikes. I really like the way they all look and all are unique. I haven't ridden the speed 4, so I can't really say much about that, but between the monster and the XB, my opinion is that the XB has the better motor (no, I'm not kidding), has better handling, and would easily walk away from the monster in the twisties. That said, I think the monster is way cooler in the looks, sound, and "feel" department, and there's way more accessories for the monster to make it your own. I've already got a ducati, so if it was going to be my 3rd bike (I've got a '74 honda also), I'd go out and test ride a speed 4 and decide between it and the XB. If it were going to be my only bike, I'd still go test ride the speed 4 and decide between it and the monster. One final consideration is that if you're riding around town a lot, the speed four will be a bit more tedious to putt around on due to the narrower powerband of its inline 4.
Good luck, and I again commend you on your 3 choices. This would make an excellent comparo.