.22 semis have always been my thing.
For years I bought every type of high end rimfire semi I could find.
Which is the best, depends on who you ask.
Collectors might pay for $20,000 a Grade III Browning takedown semi in .22 short done up by a top engraver, but they are paying for art. Obviousy these collectors feel these are the "best" semis.
The Winchester Model 63 is widely considered by shooters to be
the finest rimfire semiauto ever produced. One in good shape can be had for under $1000. A bargain compared to the engraved browning if you ask me.
I have always wanted a beretta "sport" semiauto and have never been able to locate one.
I was not fond of my anschutz semi, it was extremely fussy with ammo and had a cast receiver. Accuracy was disappointing for such a tight chamber and the compromises that come with it.
I bought a Franchi with high expectations but the quality was not much above a toy cap gun, pot metal receiver, stamped internals
Of all the semis I owned my favorite was a BRNO 581, all milled parts, very solid, really nice wood, reliable, easy to take down and a nice compact design with the bolt and mainspring slung under the barrel.
My most accurate factory semi is a Voere 2115.
I sold the Brno and kept the Voere, so for me I guess accuracy is more important.
For real accuracy from a semi you have to go custom.
Most people choose a 10/22 type receiver and action for their "custom" gun.
I suppose this is because there are so many parts available and they are so easily interchangable. An entire culture has grown up around this and as a result the most accurate rimfire semiautos you can get for any money are based on the 10/22 design.
Pro shooters in the sportsmans challenge and similar competitions use one-off recievers based on the 10/22 design, or Volquartsen receivers. Starting from there, a good smith can build a true custom gun that will outshoot any other type of semiauto for the few thousand rounds when it is in its sweet spot.
AFAIK all of the records for semiauto rimfire accuracy are held by custom guns based on a 10/22-style receiver
If accuracy is what counts most, I have to grudgingly say the custom 10/22 is the best semi at any price.
If I had an unlimited budget I might start with an olympic match pistol and install a cryoed bolt-action benchrest barrel and McMillan BR stock.
Or if it was legal maybe a straight pull biathalon action with an electric mechanism to work the bolt, or a mechanism worked by a blank or ramset charge when you release the trigger after the round has left the barrel. That would eliminate what I feel is the biggest accuracy problem with high end semis, inconsistent blowback.