I think the ArrayList efficiency is better than the Hashtable. Because the Hashtable is a dictionary type object.

It depends. Item insert efficiency? Item lookup efficiency? Item lookup by
index? Iten lookup by key? Item delete efficiency? Serialization efficiency?

This is an identical question to "What is better a linked list or a hash
table". I can tell you point blank that for searching the hashtable will
generally outperform the arraylist (especially with large sets) but the
arraylist can be more efficient at sorting (i.e. sortedlist). In order to
state anything further one would need to know the problem domain.