One pro of used stamps is that you can concentrate on proper stamps, that have been used for the reason they were created for: to send mail. But when you love stamps, and love their designs, determining what constitutes "fine used" can result in headaches and despair!
Leaving aside decisions on condition, here's a few used examples to peruse.
Is this fine used? The cancellation is light and clean, which is a pro and the stamp design is still to be admired. But you can't see the date and you can't see where the stamp was cancelled, so maybe we should opt for something like this?
You get more of the cancel on the stamp, which is great, but you lose the pleasure of admiring the stamp. So if we're not going for full cancels on the stamp, why not try this then?
It still is used, it still has a part of those nice circular cancellations, but the design is still intact. Looks good, but if you're aiming for as little cancellation on the stamp as possible, would this be okay as well, then?
Mmmhh... You see, that's why I opt for mint! And to be honest, I'm not too keen on pages of used stamps, it somehow looks not right and very untidy.
Now one thing which might, in my humble opinion, be more interesting than collecting used stamps, is collecting Machins on cover. And I don't mean the first day kind, but proper, postally run covers. You can still try and get as fine a cancellation as possible, with the added bonus that you can show for which rate the stamp was actually issued (that is, if you go for single franking covers).
Now there's a thought...........!