I've used a few pieces of POS software:
2. Compris Tricon
(Restaurant POS, I use this at work, ours is much uglier than the one pictured here - PDF Link)
3. MYOB RetailManager
I like DHPOS because:
1. It's simple
2. The price
3. It's laid out in a logical manner.
4. It will run on anything mage in the last 16 or so years.
I don't like DHPOS because:
1. No touchscreen
2. The beep is annoying.
Tricon is interesting, especially because it's a native Windows application, as opposed to DHPOS, which makes comparing the two tricky. So, I like tricon because:
1. Touchscreen capable!
2. It's more logical than MYOB.
3. If you know how, you can get out of it and into Windows and fiddle. (But you can do this in DHPOS anyway, provided you're running Windows)
4. It can be locked down to the nth degree.
I don't like Tricon because:
1. Our incarnation is ugly. Blergh!
2. The layout can be confusing.
3. The magical Sub button (for substituting items in meals) doesn't like being used on any item but the last one rung up.
4. Items jump around when you hit Total. For instance, you might have an X meal large, Y meal with Mountain Dew and a Z meal with no mayo on the burger, you hit total, and the customer then wants cheese on the Z meal, you hit Modify Order, and it moves everything around, making some buttons not behave well.
5. Possibly horrendously expensive. I know it's not free.
(Some of these things might be specific to where I work, so, meh).
I haven't used MYOB in ages, so it would be unfair for me to pick at it's fault, because they could have been fixed by now. But I did like it, it was just difficult to setup, although they do now have Retailbasics, which is more simpler, apparently.