What makes you think professionals are even qualified to make the call? Presumably you're talking typographers, graphic designers, etc - artist types who couldn't construct a proper double-blind study to save their souls.
While that may be true, there have been a LOT of studies on typeface readability and legibility over the past 150 years or so, of varying quality.
After having spent some time reading these studies, I've basically come to the conclusion that we've learned basically nothing beyond three basic facts:
(1) readers don't do well with "weird" typefaces except in ornamental or occasional use -- use something that's close to what reader are used to encountering when they will read more than a few words in the font
(2) bigger fonts make reading easier
(3) unless the font has really unusual features (e.g., some characters that don't look like "standard" letterforms), overall design can usually fix most problems -- i.e., doing things like tweaking size, space between lines, space between words, etc.
The last point is really important. Most discussions of typeface legibility have to do with things like serifs, x-height, size of holes in characters like 'o' or 'p', etc. But as long as the letters actually still have standard shapes, you can usually tweak the size or spacing to make it just as legible.
Beyond that, it's basically personal preference and what people are used to. There are studies that seem to show small effects for everything -- serif fonts are better, except when they're not. Justified text is better than ragged right, or the reverse. (Hyphens are bad, or they aren't.) Double-spacing is necessary, or it's not. Larger spaces after periods or punctuation help readability to a small extent, or they don't make a difference.
Frankly, having read a lot in the literature of typography, I think the problem with most of these studies is that overall design matters most, and I'm not talking about the design of the study (though that's important), but rather the typographic design and use case.
Some typefaces will perform better when spacing is tight, others seem better if more space is available. Some typefaces are good for people with various disabilities or vision problems, but readability may be different for those with "normal" vision. Some typefaces look better than others when a smaller size is used, but people express a different preference when text is larger... or when resolution is varied... or....
Typeface is just one of many elements of proper design. And usually reactions like "Oooh, you simply CAN'T use that font on a screen!" or "No, no, no! That works well for newsprint and headlines, but no one would ever like long text blocks with that!" are just based on what people are used to, not what would actually be more legible or readable.
For example, there are situations where people have come to expect serif or sans serif fonts. Expect people to complain if you don't use the standard choice in those situations. That's not to say one or ALWAYS better than the other -- it's just a combination of what's expected and the other design choices.