Im my personal experience with the lot of guys and girl in my office who recently made the switch, which was 5 of us, we all seemed to get quite lucky, the switches we chose we all wound up liking when we bought another 100 of them to put on a board.
I would say that with a tester, I wouldn't just test it once, I'd press them, press other ones, type on my main keyboard and go back. I took about two weeks to make a decision I was happy with because I felt my preferences change with my mood.
I also sat down and thought about what about IBM Keyboards felt good to me, and it wound up being a list like this:
1. The solid feel. (I love the feel of the metal plate, it's fantastic, makes the keyboard feel solid.)
2. The click, I like the click and feedback that the BS give me. And that they are a little harder to push down than alot of keys. I like a key that pushes back and is harder to push down. It also helps fat fingering keys, which I do frequently, but when the keys are harder to push, even if I goof, it's not as bad, and often the other pushed keys aren't even sensed.
3. The tactility, I like knowing that the second the key clicks, it actuates and sends it's signal, that's reliable and comfortable to me, so the closer that is to each other the better.
4. I like the travel distance of the Model M alot, it's what i feel the absolute perfect distance, especially for me. I don't like a short actuation like a speed silver, gold, or the other metal colors. I prefer it long, and with purpose.
5. The layout of the keyboard feels perfect. (This is more in relation to what layout you want to go for.) The key spacing on an IBM is flawless in my opinion, my rubber domes at work cause me no end of anguish because they are either chiclet, or poorly spaced 105 layouts.
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and so on.
If you can make a list of the things that you like from your Unicomp or in keyboards in general, people here can make recommendations based on just those specific attributes and possibly all of them together.
See how many of those you can list.
This won't give you a definitive answer, but at least things to try.
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More on the tester, as this is a seperate way of going about this.
My first switch tester years was just the cherries, and ran me around 15 bucks. Here's one that has more switches than mine did for 13 shipped:
A 9 switch Cherry tester. That'll give you an idea of what many switches are like, since quite a few are clones of just those, that'll give you a muscle feel to a lot of the words we use.
If you do a tester at all, press each key with all your fingers, and take your time. I didn't decide in an hour. But I can say that with a tester my decision was one I was very happy with.