A T-chart is a basic tool with two columns used for direct comparisons between two categories or sets of information. It's clear and straightforward, emphasizing differences and similarities. On the other hand, a Venn diagram employs overlapping circles to represent relationships between multiple categories or sets of data. It not only highlights commonalities but also shows how elements are unique to each category. Venn diagrams are often used for more complex comparisons involving three or more items or concepts.