I want to play slide (blues) on a lefthanded electric guitar. I can buy 3 guitars second hand. First is a ibanez les paul custom (black beauty) 1976

The second one is a Samick SAN 450 (Gibson 335 copy) build in 1992.

The third one is a Ibanez Artcore AS73.
All are lefthanded and the price are between 350 end 400 Euro's. Which one would be the best.
The Ibanez Les Paul - assuming it really was manufactured in 1976 - might be at the tail end of the "Lawsuit" Ibanez guitars. If it is, then the quality is first-rate and it has a collector following. I would go with that one if it is a "Lawsuit" Ibanez. I would need to see pictures to be certain.

The semi-solid would also be a fine guitar. Many blues players followed the lead of the late B.B. King and played Gibson (or Gibson-inspired) semi-solid guitars.

The Ibanez full hollowbody is probably going to give you a great many feedback problems; even as a slide player. So I would go with one of the other two.
"Maybe this world is another planet's hell?" - Aldous Huxley
I would go with a solid body too, feedback is usually an issue. BB King stuffed his ES 335 with cotton to help, later had a solid body model made by Gibson.. The only hollow body I've played that didn't have a big feedback problem is the Cort CL1500 I have now. It will feedback, but usually only if I turn around and face the amp or play really loud. It's not the out of control feedback you often get with a 335.

Just because I'm into cheap and vintage I'd go for the Ibanez LP model, don't know anything about the Artcore one though. Stay away from anything with a floating strat style bridge unless you plan to tune it to open tuning and leave it that way or lock the bridge down.

That type bridge is a hassle to retune, every time you change a string it changes tension on the springs in rear and changes every string. It takes 20 minutes or more to retune one to a different tuning. Even tuning to drop D will require a complete retuning.

That's why I like a fixed bridge like a Les Paul or Telecaster for slide, since I play open tunings a lot and retune at home for tinkering around. I don't like spending a half hour tuning just to doodle a bit...
Hmmm...I wonder what this button does...