I was rolling for Summer Corrin, but one time in 3 blues, I got 3 4* Effies, one neutral, one -atk, and one +atk. I was actually blessed because I had a spare brave lance+ from a spare cordelia to inherit. Now that my 5* chance is 4%, should I keep rolling or roll first on Hero Fest?
Depends if you think you need any of the characters in the Hero Fest? Do you need a Rein check? Need a blue dancer/dragon support? Miss Ryouma and need a DC red? If you answered no to these questions espically the first one you might want to consider rolling. Personally i'm rolling for S. Corrin for my flier team.
There is noone who can answer this question for you except yourself. The answer depends entirely on what you need in order to improve at the game, and what you want to get out of the game.
The second question is easier to answer: if you are a collector and want to get most/all heroes, then rolling on the time-limited summer banner makes sense (at least until you get the heroes you like, if you're not gunning for everyone). The Hero Fest units will always be available, so you will still be able to get them later (although at a much more reduced chance).
The answer to the first question is more difficult. Generally speaking, the Hero Fest focus units are better than the Summer ones (Ike, Julia and Ninian are in the very top tier, and though Genny's usefulness depends on if you like healers or not, you can always safely skip colorless if you choose, which is what I usually do). Comparatively out of the Summer heroes I think only Summer Corrin is worth hunting competitively, and that's only because she's a flier mage which are currently premium. So if you want a flier emblem it is suggested to hunt for her. But overall if you want to improve your teams for high-end Arena, Arena Assault, Chain Challenges and that other crazy mode, the Hero Fest banner is a good offer.
There is also one last important factor - number of orbs you can / are willing to throw at the game here. If we're talking a relatively small amount of orbs (80 and under) it might be best to stick to the Hero Fest banner, since you want to maximize your chances of getting one or two 5*. If you're feeling a bit more confident in your orb supply, in your situation, I'd spend orbs on the summer banner until I get a 5* and my rate resets, then I'd switch over to the Hero Fest.
Hope that helps.
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