We don't have any issues with sugar per se. What we do recommend against is consuming sugar, added sugar and all sweeteners in any significant quantity.
Artificial sweeteners should be avoided in any quantity. The quantity you consume includes not just the known sugar you eat but also the foods that have added sugar (corn flakes) vs natural sugar (a grape). Lots of snacks (even seemingly healthy ones) have added and natural sugar like dried fruit. 1 teaspoon of total sugar per day (added or natural) regardless of what kind it is, is unlikely to pose any serious long term health risk. The problem is sugar, corn syrup and things that quickly convert into glucose (white bread) is hidden in everything we eat.
In terms of least harmful sweeteners, stevia, licorice root and monk fruit are at the top of our list. Stevia in particular doesn't trigger insulin and the plant even has therapeutic effects. Monk fruit is also a plant often used in TCM. However, be sure to purchase these sweeteners in as unrefined a form as possible. Whole leaf stevia extract, whole leaf stevia juice, unrefined monk fruit extract are good. After that, we'd recommend real honey (many have added sugar water).
Things to avoid are artificial sweeteners, corn syrup, refined sugar and fruit juice (even if 100% natural) since it takes large portions of fruit to turn into juice, much more than you are likely to eat whole.