When you are selecting strangers, don't auto. Take a look at their stat distribution
For some heroes, eg, Miu, atk and crit are very, very important. But, some players have sky-high attack, while others may come with a bit more mag. This is attributed to faith, etc. But, if you select strangers manually, you can look at their stats, and add them as friends after battle.
thanks, I tried this methods, but the choices of stranger is pretty few, and powerful strangers is very rare..
I''m currently 29 lv, and I added many friends like 4* not powerful, should I remove them to find another?
The Stranger list is random, so you can keep refreshing it until you find a powerful one (check out the stats).
When you find the powerful friend and you select to use them, after stage completion there will be an option whether you would like to add that person as a friend.
If they accept your friend request, they will appear in your list and you can use them once a day.
Try to request as many powerful ally as possible, some will accept your request
For others that don't accept, you can still search for them in Stranger list but it will take some time. Do note veteran players will have their friend list full most of the time.
As for removing friends that are not powerful, I think you have to look at their potential for growth. You are currently lv. 29 so probably your own hero is not that powerful as well. To be honest, not many people with powerful hero would want to add you as friend if they don't know you, as they also have better option ( be thankful to those who added you!). I suggest you keep the friend who are active and use your hero everyday. Just delete people who are not online for more then 3 days or so. Focus on growing together! By doing this, you can build your powerful friend list in the long run. If you think about it, you wouldn't want a more powerful friend deleting you too ^^