No doubt at all it is custom paging.
Comparing the Performance of Default and Custom Paging
Since custom paging only retrieves the needed records, whereas default paging returns all of the records for each page being viewed, it s clear that custom paging is more efficient than default paging. But just how much more efficient is custom paging? What sort of performance gains can be seen by moving from default paging to custom paging?
Unfortunately, there s no one size fits all answer here. The performance gain depends on a number of factors, the most prominent two being the number of records being paged through and the load placed on the database server and communication channels between the web server and database server. For small tables with just a few dozen records, the performance difference may be negligible. For large tables, with thousands to hundreds of thousands of rows, though, the performance difference is acute.
for more details look at this link for Efficiently Paging Through Large Amounts of Data