Is it worth it to purchase any of the go software out there to play against regularly? If you guys have bought any, which ones do you guys recommend and why?

What is your approximate strength? That makes a BIG difference in any possible recommendation. Besides being something to play against, do you want what you purchased to be able to do other things (feed you problems, explain moves, etc.)

1D

All of the above

KataGo and Leela Zero are free.

LZ, for example, is stronger on an integrated GPU than older programs on a strong CPU.

I think programs are very valuable to study with. But I do not think it is a good idea to play against them, especially against the same program.

It is good learning practice to review all your games with AI. It is nice to try out variations of joseki and fuseki on the board, but it is much more effective in my opinion to try all the variations in one training session and compare them right at the moment, than to try different variations while playing games against the AI. Best combo is probably Leela Zero and the Lizzie GUI, no need to buy a program.

(So I would recommend: Dont buy a program. Play on Pandanet and review with Leela Zero afterwards, more fun and the better learning experience.)

But just do whatever you enjoy most.

I was responding to the question as asked.

And I am old enough (and in IT even back then**) to have been around for the original discussions about "free software". These were NOT about free as in free beer but a response to conditions of the day with software not only overpriced but with overly restrictive/unreasonable licenses << you SHOULD be allowed to make backups, trnsfer to a new machine, etc.>> The rallying cry was "software for the price of a book*".

IMHO most of the commercial go programs are NOT violating this. Not objectionable in the way of much of the 70's commercial software.

By all means use free software if you like.

* Being academics, "price of a book" didn't mean to them the price of a paperback thriller but the price of a typical textbook.

** Before the 2006 house fire, I even ha the journals in which this discussion took place. But it was the room in which they were that the fire took place.