Eric said:
Ah...the accurate, albeit mildly cynical answer (not a bad thing). I was trying to do the same by just predicting what others would say instead of offering my own advice.
I assure you there was no cynicism intended in my reply.
There are a ton of things to consider when buying any guitar.
To me, first and foremost, comfort. Does it fit well? Is it the right weight/size for your body? Is it neck-heavy? Does the neck fit your hands and feel good when played? Do the frets hurt your fingers after playing an hour or so? Do you feel hampered by the size of the body? Is it too light?
Then there's the sound. Does it ring out acoustically unplugged? Do you like the sound amplified? Are the pickups balanced to your ears?
The design. Are the controls in a comfortable position for you to use? (Think Telecaster...). Can you pick comfortably between the pickups? (Think Strat...).
I tend to prefer smaller/lower profile frets, larger semi-hollow guitars don't seem to hang comfortably on me when I stand playing, I can adapt to Tele standard controls, but don't prefer them, I seem to gravitate towards my Agile AL-3000 for my go-to axe, but it's not a semi-hollow.
The two I mentioned are semi-hollows, vastly different, yet each can do blues quite admirably. I do believe a person cannot give an impartial answer, an accurate answer, without a lot more information.
I know Soulstress likes B.B. King, and wants to learn the blues.
The natural tendency would be to recommend the ES-335, or rather, the Epiphone Dot, a fine guitar to be sure. Neither of those choices fit me, personally, all that well.
I believe all the choices mentioned thus far are fine axes, but if we go back to Soulstress's original question.........
"Assuming we are talking about semi-hollow body
What is the best brand for a blues guitar ever?
What is the best brand for a blues guitar under $500?"
......... I would have to revert to my original answer.........
"It would be the brand you'll pick up and play, enjoy every day, and fits you the best in every way."
And the only way to know the answer for a particular person would be try out a bunch of semi-hollows under $500 and see which one meets the criteria.