Question: is zeref the strongest in fairy tail?
Answer: Now, Natsu is the strongest demon Zeref ever made but he is still not the strongest character as he lost many times to Gildarts, Laxus, Erza etc. ... So, there is no one stronger than Zeref but Natsu will be the one to defeat him (hopefully) but with others` help. So you can say that Fairy Tail Guild is the strongest.