UK 8
Germany 7
US 6
Canada 6
Poland 5
Italy 4
Spain 4
France 3
People think Poland is very pro-Ukraine (which is somewhat true if you look at aid as a percentage of GDP that they've given so far) but they also
stopped arming Ukraine over a trade dispute, so they lose many marks for that.
US and Canada have both contributed about 0.3% of their GDP on arming Ukraine - it's not bad, & they are both definitely amongst the top contributors due to the aggregate size of their economies, but they can do a lot more.
In comparison to their economic size and geopolitical power, UK and Germany have definitely done the most, but Germany loses a mark for trying to force Ukraine to negotiate. So I guess UK would be the most pro-Ukraine country.