I've seen Arial mentioned a few times, and it needs to be said again: in general, the graphic design industry does not look kindly on this Helvetica hybrid.
If the graphic design industry is anything like all the classes I took back in the late 1980s and all the people I've known in the business since then, the graphic design industry does not look kindly on ANYTHING
popular with people "pretending" to be graphic designers. If Frutiger (another vote from me for that one, as I LOVE that font family) is the bees-knees with people who don't have much training in leading, kerning, contrast, color, the balance of positive and negative space on a palette/page, etc., then graphic designers will hate/mock/avoid it. If everyone in the main-stream thinks that Arial is a "scourge," I'll all but guarantee you that it'll start appearing in more designs out of graphic design shops...just to thumb their noses at all the "cattle" or "lemmings" that some perceive the rest of us to be.
I'm not poking fun at others either...as what I do in the greater map design field probably has a LOT more to do with graphic design than it does with traditional cartography...and my classroom education reinforces that distinction.
It's like when I was in high school. Hanging out with the kids who "rebelled against the mainstream"...listening to different music, dressing differently, etc. Mocking conformity...when they themselves were conforming to one another (or at least the leader(s) of that group and what they liked, what they listened to, etc.) and giving in to peer pressure.
If your clients and end-users love Arial and/or it works very well in establishing a look/pop while enhancing usability, use it. Don't let others get to you for those decisions...and don't convert all your design text to "CartoTalk Narrow" just so that others in the industry will give you a passing grade.
1. End-users and legibility
2. You and your own preferences
3. Your peers in the industry
That's how to prioritize decisions such as this, IMHO. Don't fall into the trap of "3-2-1." Being a "conformist" and/or not running with the cool kids is A-OK too...as long as you're getting the job done, your clients are happy, and your end-users are being very well-served.