Personally I don't necessarily agree that low-sugar=best here is a list I pilfered from Live Strong

Apple (sliced)
Apricot (4 oz.)
Blackberry
Blueberry
Boysenberry
Cantaloupe
Cherry (sour, sweet, 10 medium)
Coconut meat (1 oz. or 1 cup shredded/grated, not packed)
Coconut milk
Currant (red, black, white)
Elderberry
Gooseberry
Grape (10 medium)
Honeydew melon
Kiwi fruit (1 medium)
Kumquat (1 medium)
Lemon/Lime (2 inch diameter)
Lemon/Lime Juice (1 oz)
Mulberry
Orange (sections, without membrane)
Peach (1 med, 4 oz.)
Persimmon (American, Japanese, 1 medium)
Pineapple (1 oz)
Plum
Raspberry
Strawberry
Tangelo (1 medium)
Tangerine (1 medium)
Watermelon

Except where noted, all have less than 10 gm carbs in a half cup serving.

You can use the handy little Nutrient Search Tool on the NutritionData web site to find out this sort of info & lots more.

Here's the search for 'lowest in sugars' within the 'fruits and fruit juices' food category.

Sugar is pretty irrelevant, you need to worry about carbohydrates and glycemic index. On both those grounds then berries such as strawberries, blueberries and raspberries are best.

Are you metabolically well? If you have no blood sugar issues and respond to "paleo approved" carbs, then moderation of any fruit is going to be okay. However, it's fructose that you want to limit (the best you can.) I would rather try to go after berries and other low fructose content fruits.

Here is an awesome post showing fructose content of all major fruits: http://becknaturalmedicine.blogspot.com/2010/04/fruit-fructose-content.html

if you go by Sugar content per ounce here is the list

Fruit (Raw) (3 oz)Sugar Total (g) Calorie Total
Strawberries 4.27g 27cal
Papaya 5g 33cal
Watermelon 5.3g 26cal
Grapefruit 5.9g 27cal
Cantaloupe 6.7g 29cal
Nectarines 6.7g 37cal
Peaches 7.1g 33cal
Kiwis 7.6g 52cal
Guavas 7.6g 58cal
Apricots 7.9g 41cal
Oranges 8g 40cal
Pears 8.3g 49cal
Plums 8.4g 39cal
Pineapple 8.4g 43cal
Blueberries 8.5g 48cal
Apples 8.8g 44cal
Tangerines 9g 45cal
Bananas 10.4g 76cal
Cherries 10.9g 54cal
Pomegranates 11.6g 71cal
Mangoes 12.6g 55cal
Grapes 13.2g 59cal
Figs 13.8g 63cal

You'll want to look at the gucimic index more than sugar content. Marks daily apple has a good breakdown but I'm not at a pc to link you in. Just search the site for glycimic index and fruit

Lemons, limes, strawberries, boysenberries, blackberries, cranberries and raspberries are all very low. (also tomatoes, which are also a fruit)

Theres good reasons to avoid high sugar fruits.

Modern fruits have far more sugar, and far less nutrients than their wild counterparts, fructose is implicated in diabetes, insulin insensitivity, liver troubles and belly fat obesity (fructose is processed by the liver unlike glucose which requires no processing and does not create belly fat = although it can still produce some insulin sensitivity).

Fructose is responsible for many or most of the ill effects of refined sugar. This is connected to how we now know high fructose corn syrup is worse for you than refined sugar.....Sugars also feed bad bacteria.

One should either eat only moderate fruits and preferably low sugar IMO.

Berries seem to be the most like their wild counterparts in terms of sugar content, unlike most fruit in the supermarket which is quite high. Great thing is you can get frozen berries all year round...

One only needs to look at -

a) the actually availability of wild fruits in most enviroments and

b) their sugar content vs modern agriculturally altered fruits and

c) studies showing the harms of high fructose consumption, to realise that this "eat lots of fruit" malarky is dead wrong.

Yes they have great anti-oxidants, and good vitamins, no we are not supposed to eat them in large quantities and ignore their sugar content...