We have a mix of sizes and shapes of tables, all donated. We've recently replaced the donated chairs with stacking metal chairs. Particular people gravitate towards different tables.
Rectangular tables seem to encourage smaller conversational groupings.
That's when the people either side of me aren't leaning around me or craning over my head to talk. It becomes difficult at higher noise levels. Rectangular tables allow smaller conversations in noisier conditions, with one person at the end and two others on the sides. Two of us were able to lift one quite easily. Some stacking chairs tip backwards easily.