That depends on your level. If your level is basic, the best Garmin for you is the FORERUNNER 5. If you have an intermediate level, the best Garmin is the FORERUNNER 245 and, if you are an advanced level, the model will depend on whether you like maps and use them often.
If you love maps, the Garmin Forerunner 945 and if you don't like them much, the Garmin FORERUNNER 745 would be the perfect model.