Which is the "BEST" deep learning model for "Custom" object detection for images & real time. YOLO v3, v4, v5, EfficientDet? Whenever I look for object detection model, I find YOLO v3 most of the times and that might be due to the fact that it is the last version created by original authors and also more stable. In 2020, a new author released unofficial version called YOLO v4 and just after 5 days, another author launched YOLO v5. I am confused that if I have to chose one of the models, which one should I chose? EfficientDet is better than YOLO v3 in my opinion but there is very less talk about that. Is there any other model which is better than thsese? I want to know which models should I chose if I'm detecting objects in images and videos respectively. When speed is not an issue, which one is the best model and when speed is an issue  like in videos, which one should I use?
There are many subtle differences between yolov4 and v5 other than speed like YOLOv4 exceeds YOLOv5's performance on the COCO benchmark.this link will help you explain.
YOLOv4 VS YOLOv5.
I dont know much about EfficientDet.
Here's YOLOv3 Versus EfficientDet for State-of-the-Art Object Detection
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It explains quite nicely difference between the two.