‘ Men said to them: “A great army is gathering against you”: and frightened them: but it (only) increased their faith. They said:
“For us Allah sufficeth and He is the best disposer of affairs.” ‘
The Holy Qur’ān – Surah Āl Imrān (3:173)

Transliteration: Hasbun allaahu wa ni’mal wakeel
Translation: Abdullah Yusuf Ali

Sigh.
I always said “Hasbunallah…” but then earlier this year, I read it as “HasbIYAallah…” and the meaning was the same or similar. SO I don’t know which one is correct or what is the significance between the two. *Sigh*
There are approximately 12 occurrences of this word (Hasb) in the Qur’an.
Both variations you mentioned are correct and occur as indicated below.
The only difference is between the personal pronoun suffixed to the end of the word ‘Hasb’. The two you have mentioned are singular (me) or plural (us).
To be precise:
‘HasbeyAllah …’
This means ‘Allah is enough for ME.’
This can be found in:
Surat At-Tauba (9:129) and
Surat Az-Zumar (39:38).
‘HasbunAllah …’
This means ‘Allah is enough for US.’
This can be found in
Surah Al-Imran (3:173);
Surat Al-Ma’ida (5:104) and
Surat At Tauba (9:59).
Hope this helps : )
wAllahu A’lam.
Thanks for the info