Finding the translator app that suits you best is not easy. What makes for the best translation app ultimately depends on your needs.
If you value speech recognition and voice output, take a look at SayHi Translate. If you just want a single word or phrase translated from English into another language then Linguee and PONS are highly recommended due to their huge vocabulary.
Smartwatch owners should take a look at Microsoft Translator or Google Translator because both apps are based on modern hardware. For a good all-rounder, either one would be a good choice. Due to the large number of supported languages, the apps are particularly versatile and ideally suited for everyday use.
DeepL is more of an insider tip. Although it supports fewer languages than some of its competitors, the quality of translations is outstanding.