Native Lua

Using table.sort is okay, but inefficient. You're doing a needlessly expensive operation when a single loop through of the list is sufficient.

If you want to find the maximum of a list of numbers, use

math.max(unpack(list))

Note that this will only work if the list is less than 8000 elements big, and if they're all numbers.

Improving on native Lua

If you're dealing with more complicated data types / structures, or if you want to deal with longer lists, you're going to have to get a bit fancier.

function findMax(list, comparator)
    comparator = comparator or math.max
    currentMax = list[1]
    for v in pairs(list) do
        currentMax = comparator(currentMax, v)
    end 

    return currentMax
end

This should do what you want. Using it in the simple case is easy. If comparator is left blank when calling it, it will default to standard math.max behaviour:

a = {1, 2, 3, 4}
b = findMax(a)
print(b) -- Gives 4

Getting spicy

What about if we have a list of players, and we want to find the one with the highest score?

players = game:GetService("Players"):GetPlayers()
highScorer = findMax(players, function(playerA, playerB)
    if playerA.leaderstats.Score.Value > playerB.leaderstats.Score.Value then
        return playerA
    else
        return playerB
    end
end))

Basically, comparator is any function which takes two values and returns the largest.

For example, if we wanted to select the heaviest brick:

function heaviestComparator(a, b)
    if a:GetMass() > b:GetMass() then
        return a
    else
        return b
    end
end

heaviestBrick = findMax(bricks, heaviestComparator)

you can use math.max() which returns the greatest value of them given, though it isnt only limited to 2 values but can store multiple (3, 4, 6, 11...), since it uses variadic arguments.

local num1 = 16
local num2 = 25
local hum3 = 6

print(math.max(num1,num2,num3)) -- prints 25

variadic arguments

For a gui that displays who has the most of any score, math.max is the most efficient method, but if you want to display, say the top 3, 5 , or 10, something on the lines of table.sort().

table.sort

What table.sort does is sort/organize a table using its default procedure which is <. However, that can be changed like such:

local kos = {1,421,32}

table.sort(kos,function(a,b) 
    return a>b 
end)

for  _, plrKos in next, kos do
    print(plrKos)
end--421,32,1