Super Saiyan 4 vs Super Saiyan Blue in Dragon Ball Heroes, which transformation is stronger? Super Saiyan 4 vs Super Saiyan Blue is being reported to appear fighting in Dragon Ball Heroes. Dragon Ball Heroes it's an official non canon Dragon Ball videogame and manga. Which transformation is stronger?

Note: before marking the topic as "opinion based" notice most transformations in Dragon Ball are officially ranked in order of power through the anime, manga and official guides and websites. 

(with the exceptions of Super Saiyan Rage and Legendary Super Saiyan / Super Saiyan Berserker that nobody can assure exactly where they are)

(Oozaru &lt; SSJ1 &lt; SSJ2 &lt; SSJ3 &lt; SSG &lt; SSB / SSRosé &lt; UI)
In Japan, the Dragon Ball Heroes website did a poll on who fans thought were the strongest characters and forms in the game. You can view the same here. As per the source, SSJB Goku is considered to be the third strongest character in the game while SSJ4 Goku is considered to be the ninth strongest character. SSJB Vegeta is considered to be the eleventh strongest character while SSJ4 Vegeta is the seventeenth strongest character on the game. So based on  the poll only SSJB is > SSJ4.However, certain characters in the anime like Whis , Beerus and even Omega Shenron, who are clearly superior to SSJB/SSJ4(In Super, GT) Are a lot lower down the list(Even below Yamcha). So there isn't really a perfect answer to your question.
Final ListTime Breaker Bardock
SSJ4 GT Gogeta
SSJB Goku
LSSJ4 Broly
Darkness Towa
SSJ3 Time Patrol Bardock
Tarble
SSJ4 GT Gohan
SSJ4 GT Goku
Super 17 (18 Absorbed)
SSJB Vegeta
Super Mira
Golden Frieza
LSSJ Broly
SSJ3 Vegetto
Majuub
SSJ4 GT Vegeta
Towa
SSJ2 Teen Gohan
SSJG Goku
Yamcha
Supreme Kai of Time
Syn Shenron
Whis
Runaway Mira
Amond
Resurrected Dabura
LSSJ3 Broly
Omega Shenron
Angered Beerus