The best thread count in sheets is determined by yarn size aka “yarn count” and not solely by the total number (sum) of thread. Yarns come in a variety of sizes (count) and materials. Based on which “yarn count” is picked a new fabric is the out come. Also, more than one yarn count “yarn size” can be used in weaving single fabric. The main rule is having a well balanced horizontal and vertical yarn in terms of weight and number of yarns used.
If Percale is your pick then 300 Thread count percales is particularly good when woven at single pick insertion using 60s. Percale is matte one over one plain weave and cannot be made at higher thread counts like 600 for example.