Anything over 180 thread count is considered a superior weave and should give years of wear assuming the cotton thread used is a reasonable quality cotton. The term percale refers to a closely woven fabric with a thread count of 180 or greater using a good quality cotton. A percale sheet should be smoother and more durable than regular cotton sheets. I would always recommend a percale for the bottom sheet if it is within your budget as this takes the most wear. Remember the percale label is used for polycotton duvet covers and bed sheets as well as cotton duvet covers and bed sheets.
In this photograph I have put a percale sheet, which is a 200 thread count, on the left and a regular cotton pillowcase on the right. Both have been in use in my own house for in excess of five years, (and probably a lot longer) so they will have been through the wash many times which means the threads will now have “fluffed out”. If you look closely you will see the difference in the weave. There are about fifty or sixty threads per square inch more in the percale. The percale is using a finer thread so more threads will fit in a square inch. The percale has a crisper feel to it whereas in the regular cotton on the right, the cotton is much softer and pliable, though it may not look it up close. In case anyone is wondering, the colour difference is nothing to do with the quality of the cotton. They just happen to be from two totally different suppliers and batches. If it was paint I was talking about, I would probably describe the regular cotton as a soft white or winters white or some such colour.