Which candles to choose? Let's start with candlesticks.
But how to choose the most suitable candles and how to position them? Let's start with the basics: the first thing to do is to place them in such a way that they don't obstruct the view between diners. To do this, you could use very tall candlesticks, so that the bulkiest part of the arms and the candles are up above the eyes. The arms of the candlesticks will also provide a wonderful support for placing small green branches.
This is a solution that will give your table a very formal air and, personally, for Christmas I prefer a slightly more intimate and convivial atmosphere. This is why I generally prefer the candle flame to be positioned lower down, as I find its dance hypnotic and relaxing for those at the table.