Hi,
#1. Since
accent is a countable noun, we need
'a' for both
heavy accent and
heavier accent.
#2. I prefer
'hesitancy in responding'.
Besides the above comments, both sentences have a run-on problem. There are more than one way to reword them; and here is my suggestion:
Student1 had a heavy accent. S/he showed much more hesitancy in responding to the question, and expressed less confidence than student2.
Student1 had a heavier accent than student2. S/he also showed muchmore hesitancy in responding to the given question, and expressed lessconfidence in speaking English.