Which unit will he not draw with 18 points? I don't see a single archery tag in the state that can't be had for 18 points. Of course there is always the chance that a few high point holders decide they don't want to wait on a rifle tag and jump pools, but last year there was not a single unit that 17 points didn't guarantee a LE archery elk tag. So yes, your 18 points absolutely should be enough to draw whatever tag you want. Should is the key word there, because we never know with tag numbers and what high point holders will do. But you can assume you are safe to draw a tag and go for it.
Another thing people always say about Utah's archery elk hunt is that it sucks. Every year a good number of the best bulls taken off every unit come in the archery hunt. And every year, some of the very best bulls (if not THE very best bulls) killed in the entire state are during the archery hunts. So at least some people would disagree those hunts suck.
Personally, I would go with a unit that you are going to be able to spend a lot of time scouting and hunting. If a unit is too far away, it becomes very difficult to break away and scout. Having such a long season, it's possible you wouldn't plan to stay out the entire season, so that makes far away units difficult as well. At least it would for me.
It also may depend on how you want to hunt. How you hunt some units is very different than others. A lot to factor in besides what is "best," as that gets pretty subjective really quickly.