The major difference between a good man and a devotee is that, a good man does everything for his own self where as a devotee does everything for his Lord. Selfless service of God is the mark of a true devotee. Therefore, while a good man has to take care of his karmic balance himself, the Lord takes care of it for the devotee and bears his necessities giving what he needs and preserving what he has:
ananyāś cintayanto māṁ ye janāḥ paryupāsate
teṣāṁ nityābhiyuktānāṁ yoga-kṣemaṁ vahāmy aham [BG - 9.22]
But those who always worship Me with exclusive devotion, meditating on My transcendental form – to them I carry what they lack, and I preserve what they have.
So a devotee is superior because while a good man can get entangled in the maya and karma of the world and fall down, a devotee never perishes. No matter what, someway or the other the Lord will help his devotee. So Shri Krishna makes this declaration openly in the Gita:
kaunteya pratijānīhi na me bhaktaḥ praṇaśyati [BG - 9.31]
- O son of Kuntī, declare it boldly that My devotee never perishes.
And the most important point is that a good man by his actions, however good they may be, can never get over maya. It is because the divine maya of Lord is very difficult to overcome and only the devotees who surrender to Him get across it:
daivī hy eṣā guṇa-mayī mama māyā duratyayā
mām eva ye prapadyante māyām etāṁ taranti te [BG - 7.14]
This divine energy of Mine, consisting of the three modes of material nature, is difﬁcult to overcome. But those who have surrendered unto Me can easily cross beyond it.
So a non-devotee will only be wandering between higher and lower planes of existences as per his karma without getting liberation.
And another point is that, a good man can mitigate his sins by performing expiatory actions if available, but it is very hard and taking care of karma is a very delicate and risky business. However, a devotee gets liberation from his past sins easily by fully surrendering to God:
sarva-dharmān parityajya mām ekaṁ śaraṇaṁ vraja
ahaṁ tvāṁ sarva-pāpebhyo mokṣayiṣyāmi mā śucaḥ [BG - 18.66]
Abandon all varieties of religion and just surrender unto Me. I shall deliver you from all sinful reactions. Do not fear.
Is a devotee more dearest to the supreme being than a good man?
Yes, he is. Generally God is impartial and He is same to everyone. But because a devotee loves Him and serves Him, a devotee is more dearer to God than any other person:
samo ’haṁ sarva-bhūteṣu na me dveṣyo ’sti na priyaḥ
ye bhajanti tu māṁ bhaktyā mayi te teṣu cāpy aham [BG - 9.29]
I envy no one, nor am I partial to anyone. I am equal to all. But whoever renders service unto Me in devotion is a friend, is in Me, and I am also a friend to him.
na hy asyāsti priyaḥ kaścin nāpriyo vāsty amāninaḥ
nottamo nādhamo vāpi sa-mānasyāsamo ’pi vā [SB - 10.46.37]
For Him no one is especially dear or despicable, superior or inferior, and yet He is not indifferent to anyone. He is free from all desire for respect and yet gives respect to all others.
How much God loves His true devotees can be guessed from what Shri Krishna once told to Uddhav thus:
na tathā me priyatama ātma-yonir na śaṅkaraḥ
na ca saṅkarṣaṇo na śrīr naivātmā ca yathā bhavān [SB - 11.14.15]
My dear Uddhava, neither Lord Brahmā, Lord Śiva, Lord Saṅkarṣaṇa, the goddess of fortune nor indeed My own self are as dear to Me as you are.
God loves His devotees so much that He wants to make the whole world pure by the dust of the feet His true devotees and always walks behind them:
nirapekṣaṁ muniṁ śāntaṁ nirvairaṁ sama-darśanam
anuvrajāmy ahaṁ nityaṁ pūyeyety aṅghri-reṇubhiḥ [SB - 11.14.16]
With the dust of My devotees’ lotus feet I desire to purify the material worlds, which are situated within Me. Thus, I always follow the footsteps of My pure devotees, who are free from all personal desire, rapt in thought of My pastimes, peaceful, without any feelings of enmity, and of equal disposition everywhere.
Can a great misery happen to a devotee?
Yes, as long as prarabdha karma is in effect anything can happen to a devotee as per his past actions. Someone may have become a devotee in the present life, but he still has many past actions to experience. Hence, as effects of the past actions any kind of misery can happen to a devotee.
Even if there is no misery in prarabdha karma, a devotee may have to face difficulties as a test from the Lord. In Bhagavatam Shri Krishna says how He bereaves His devotees from material wealth, friends, etc. Also if we see the life of saints many of them faced difficulties in life. But all these are in the primary stages or sadhana stages. Once a devotee becomes God-realized, a devotee can get rid of any misery if he wants just by praying to God and the Lord also always protects him. Nevertheless, be it God or a devotee, all respect the laws of Karma and face results of their actions accordingly.