Manga 21479 Sword Art Online Userrecs

similarities -they have the same author -Both deal with Virtual Reality -Light Novel even Involves A Crossover in which both of the main characters meet. Main Differences are in the main character design both in virtual reality and outside of it. Kirito is portrayed more of the dark swordsman, while Haruyuki is more of a shining knight. While outside of the Virtual Reality, Haruyuki is overweight and shy, while Kirito is semi-underweight (from spending 2 years in virtual reality) and outgoing. Also Sword Arts Online is more like a team deathmatch, where dying in game equals dying in real life while Accel World is more of fighting to keep your Accel abilty.  

The Incarnation System in Accel World is based on Alicization, also in volume 4 Accel World mentions NerveGear. besides that there are still many connections from Sword Art Online to Accel World. 

Both characters are transported to an alternate world but only Shield Hero is a true isekai. They also somehow end up as solo players along the way after an incident happened that ruined their lives and team up with a beautiful girl. The differance being that SAO actually has theme of relationships and how our relationship in the virtual world affects the real world while Shield Hero is merely a deconstruction of rpg themed anime in that mc has one of the most powerful weapons in the game but it's too useless to use effectively without a backup.