Nginx + Gunicorn is what we use. It has worked great for us. We have also tried uWSGI, a waitress for our production and Nginx + Gunicorn have been sure shot winners in terms of scalability and performance.

This is our gunicorn.conf that ensures gunicorn does not cause memory leaks

    import multiprocessing
    import os
    import random
    from getenv import env

    def pre_fork(server, worker):
       f = '/tmp/app-initialized'
       open(f, 'w').close()

    bind = 'unix:///tmp/nginx.socket'
    workers = os.environ.get('WEB_CONCURRENCY', 
    (multiprocessing.cpu_count() * 1 - 1))

    MAX_GUNICORN_REQUESTS = env('MAX_GUNICORN_REQUESTS', 100)

    if MAX_GUNICORN_REQUESTS:
       max_requests = MAX_GUNICORN_REQUESTS

    MAX_REQUESTS_JITTER = env('MAX_REQUESTS_JITTER', 25)

    if MAX_REQUESTS_JITTER:
        max_requests_jitter = env('MAX_REQUESTS_JITTER', 25)