I am just wondering would it be classed as Kufr or Nifaaq or something else if a person who believes in Allah (swt) and the Messenger (pbuh)
and all the articles of faith with utmost certainty (not a shadow of a doubt!), and does his best in ibadaah and other good deeds as much as he is able, but deep in his heart
he wishes he did not exist.
***No that is neither Kufr nor Nifaaq, what you have stated is merely the result of reflecting on the reality of this life and the difficulties we all have to go through as believers. It is this type of fear that will propell the muslim to be conscious of Allaah to fear His wrath by abstaining from everything Allaah and His Messenger [sallallaahu alayhi wa salam]forbade and an encouragement to do everything that Allaah and His Messenger [sallallaahu alayhi wa salam] commanded or encouraged. There is no doubt everyone from amongst the believers would love an easy reckoning or no reckoning at all and Allaah and His Messenger [sallallaahu alayhi wa salam] taught us ways in which we can lighten our reckoning as it comes in the authentic hadeeth narrated by Abu Hurairah [radiya Allaahu anhu] "whoever believes in Allaah and the last day, let him say that which is good or remain silent" [Collected by Bukhaaree and Muslim] So there are ways and means to lighten your reckoning.
He wishes Allah (swt) did not create him at all.
***That is a result of your fear but also temper that fear with hope and having husnu dhann billaah [have a good opinion of Allaah] reflect upon His names and Attributtes and Qualities. Know that He is Merciful, Forgiving, Gentle, Loving, by reflecting on those names and attributes and qualities should fill your heart with hope. We as Muslims worship Allaah upon love,hope,and fear. We combine all three otherwise we fall into deviance.
He would rather not exist at all than to go through the pains of Dunya, Grave, Judgement, Siraat etc and given the choice he would rather be a insect (with
a life of a few days but little pain and no accountability) or a Angel who can do no wrong or simply not exist.
***I totally understand how you feel, such is the way of the believers, when we reflect on the Kitaab and the Sunnah there is no recourse except that we travel throughout this life upon two wings, the wing of hope and the wing of fear. It has been said by some of the people of the past,"whoever worships Allaah with love alone is a Zindeeq [heretic]. He who worships Allaah upon hope alone is likened to a Murjiah, and he who worships Allaah upon fear alone is a Hurooree [khawaarij] but he who worships Allaah upon love, hope an fear then he is a Mu'min Muwaahid."
Is this kufr or nifaq, or something other?