I'll be honest there is no comparison to be made, not really anyway. I think the Game of Thrones/Wars of the Roses parallels have been massively exaggerated by people who want to find a real historical parallel to their favourite fictional series.

Now there's nothing inherently wrong with that, but it does mean that people end up searching for historical equivalents to the characters in GoT and using faulty analysis to find similarities. People wanted to find an historical figure to compare Joffrey with and thus they settled on the only late teenaged figure in the time period to compare him to.

By all accounts Prince Edward was a brave young man, the very fact that he was killed in battle, fighting for his father, aged only 17 would seem to confirm this. But the reason that there is a paucity of sources on him is that he was an inconsequential figure in history. His father Henry VI had been successfully deposed in 1461 by Edward IV and the only reason the Battle of Tewkesbury took place was because the Earl of Warwick had conspired to depose Edward and place Henry back on the throne, in much the same way he had conspired with Edward to depose Henry a decade earlier.

As much as I love GoT and as interesting as I find the Wars of the Roses there is no parallels between Joffrey and Edward other than they both died as teenagers. Joffrey became King, Edward didn't. Joffrey was extremely cruel, Edward wasn't (or If he was there is no evidence of it, since he never held any power that would have allowed his cruelty to manifest). Joffrey was a coward who never have led his troops (Battle of the Blackwater) while Prince Edward's courage in doing so is what got him killed.