Have you gotten involved in competition acro yet? What's your current acro experience? If you have not yet gotten involved with competition acro, it would be a little premature to be looking for an airplane that you can fly Unlimited in. I don't mean to discourage, but very few pilots end up competing in Unlimited. Becoming competitive at that level takes years and a very high level of dedication, and lots of coaching/critiquing. Many people enter the sport wanting the highest performing airplane possible, which can take them to the highest levels. It's hard to say how far you will go until you've been involved for awhile. You can get there, but in the meantime, I'd look at an airplane that will serve your purposes right now. It will take years to truly outgrow even the Yak 55. So right now, buy what you can afford, and what interests you. You are not stuck with an airplane forever, but there's also nothing wrong with buying the most performance you can afford, even if you never end up needing that much performance (flying Unlimited). Many pilots never fly their Extra 300's beyond the lower to mid categories in competition.

But since I've never flown any of the airplanes you list, I can only provide my observations as someone who has watched and judged these airplanes at contests. The mid-wing Extra 300 is a good 2-seat performer if you need/want two seats. It is lighter and slightly better performing than the 300L. Probably cheaper too, since they are older. But recreational acro pilots prefer the improved visibility and creature comforts of the 300L.

The 300S seems to be the best performing Extra short of the new 330 airplanes. Lighter than the 300 and with larger ailerons I believe. These are still very capable of being competitive in today's Unlimited category. If you don't need two seats, this would be a great choice.

I don't know much about Suks, but the 26M is of course an Unlimited capable machine.

The Yak 55 could be coerced through the Unlimited sequences, but will be more competitive up through the Advanced category. They are a bit heavier of course than the Suk, and roll slower. Don't know much about maintenance. They can be had much for much less money than the others of course.

Good luck in your search.