Ivo Karlovič hit the most aces during 2014 so far (until August 2014), according to ATP. In total, he scored 885 aces in just 50 matches. This means incredible 17.7 aces per match on average.
John Isner came second with 772 aces (average 16.8 per match) while Milos Raonic placed third in 2014 (total of 752 aces implying an average of 16.3 per match).
John Isner hit the most aces (112) within a single match. It was in the 2010 Wimbledon first round, John Isner hit 112 aces in a match against Nicolas Mahut, who himself hit 103 aces, by virtue of it being the longest match of tennis ever played in terms of both time taken (11 hours 5 minutes) and number of games (183).
The record for the most aces in a tournament is held by Goran Ivanišević who hit 213 aces en route to winning Wimbledon in 2001. Goran Ivanišević holds the record for most aces served in a year with 1477 in the 1996 season. He also holds the record for most career aces with 10,183