I have no experience with the Venture 21, but we purchased a Mac 26S at the end of August of this year and love it. Hard to imagine a boat better suited to our circumstances.
We decided we wanted a boat that we could trailer behind our minivan so that we would not have to rely on marina services should we need to haul it out, or if we decide we want to sail in on another lake. I trailered it all the way from St. Louis to Dallas with no worries.
We needed an affordable boat, which this one was. 1994 model, very well taken care of, for $6900. Came with all kinds of extras, and was ready to sail with only a little work needed on the motor.
Improvements and maintenance are quite affordable, thanks in large part to Blue Water Yachts. Todd owns and sails one of these, and has become my guru regarding modifications and repairs. I find that their prices are excellent, as is Todd's advice.
The boat is a joy to sail. I find that it is very well-balanced with little if any weather helm in most circumstances. Easy to single-hand, and accelerates nicely. I find that I am out-sailing or at least keeping up with most of the boats I pit myself against, even when they are flying 125-150% genoas. Of course, they may not really be trying all that hard, right?
The cockpit is roomy. I have seen boats much larger without as much cockpit space.
I have gotten all kinds of compliments on the boat itself. The lines are clean and I think the standard sail package is just perfect for the boat.
With the centerboard design, we can sail pretty much anywhere we want without worrying about running aground. This is a big plus for us.
We have gone "lake camping" with the boat once and are eager to go again. The aft berths are plenty big. The forward berths don't allow enough foot room for two adults, IMO, so I would say three adults, two kids max unless someone wants to sleep in the cockpit, which would be doable I suppose.
All that said, there are some caveats:
It does not have a stand-up cabin. The pop-up allows a person to stand in the cabin, and that pop-up can be enclosed with windowed plastic cover, but moving elsewhere in the boat (i.e. to the head), will require stooping.
The 26S is a water ballast boat, and is self-righting, but can be capsized. Sailing a boat without a keel is not as forgiving. The plus of this is that it makes you pay attention to the balance of sail power, thus you end up sailing the boat more optimally than if you just were relying on the keel to keep things steady.
The hardware on the 26S is not as robust as what you will see on most other boats. I would not want to take this boat out of unprotected waters except close to the coast with full confidence that weather for the sail was not going to get nasty. I sail on a medium-sized lake (Grapevine) and feel no need or desire to go out in winds greater than 25 MPH.
The 26S has been described in at least one boat review as a "boat kit". It has provisions for adding a traveler, jib sheet tracks, and other improvements, but this is left up the the owner. If you like doing this sort of thing (as I do), it can be a plus.
I carefully weighed my options and selected this boat for the reasons mentioned above. So far I have no regrets.