Carb content of red wine?
Between 1-4 grams per 5 oz/150 ml glass for dry wine types
so not very high in carbohydrates.
How about the sugar content in wine?
About 1-2 grams per 5 oz/150 ml glass
for dry wines
and dessert wines can have up to 8 grams.
How many calories in a glass of wine?
Around 120 calories in avarage and most of it is from the alcohol
and not carbs/sugars.
A brut Champagne is commonly less at around 95 calories/glass.
Wine compared to beer when it comes to calories?
Calorie content varies but in general wine contains less calories than beer and the drier the wine the less the calorie count is. White or red is not as much of a factor as the sweetness of the wine is.
A really dry/brut glass of champagne is low in calories. 
So what type of wine is best if you are on a diet?
A dry wine.
So for reds go for Sangiovese, Tempranillo, Pinot Noir or a Cabernet Sauvignon.
If you prefer white wines you can go for Muscadet, Sauvignon Blanc, Pinot Gris or even a Chardonnay.
Another good choice as mentioned above is a sparkling wine like Champagne or Prosecco as long as it is brut, extra brut or brut nature/zero dosage.
If you eat healthy and exercise, a glass of wine every now and then will not hinder your progress if you are trying to loose some weight.