You can see here how price developed during the last years:
https://www.gw2spidy.com/item/77604
Summary: prices drop once wintersday starts and start climbing again afterwards, but it takes until May until they are high again.
In addition, this year the price is pretty low and might rise only 1s per gift.
There is this website with up-to-date numbers how to earn gold with stuff. I linked the karma-page below:
https://fast.farming-community.eu/conversions/karma
There are theoretical profits listed there, but some are bothersome to make. For example putting 4 rare karma-weapons in the forge for 340 Karma and selling the result for an avg-price of 19s in TP. In theory that's 56s profit for 1k Karma, so 1400g profit, but you don't want to do it 7 thousand times plus prices may drop.
However, it also lists Wintersday gold/Karma profit. The 700 wintersday gifts come out at 6s40k/1000 Karma at the moment. Buying frostbitten gathering tools have the highest profit, but I guess you get the gold by using them and selling snowflakes, so again nothing quick.
"Recipe: Bringer's Intricate Gossamer Insignia" can be bought at the vendor for 3g+15,001Karma and be resold on TP for 6g17s, making a profit of 2g25s, which is 15s per 1000 karma and double as much as wintersday gifts... however, TP-prices fluctuate at the moment and less items in total are sold. Also, waiting to sell them until May may triple the price.
The weapon-skin toy-dagger: if you don't want to wait it has almost the same win-rate as wintersday gifts, but prices usually drop after wintersday
As a side-note, the Pact Scout's Mapping Material you can get 6 of each day costs 5250Karma. With 40 of them you can fill a map-bonus-reward track which grants materials that you can sell on TP. The rewards change in a 8-week cycle, but there is a website listing the current materials and profits here:
https://wiki.guildwars2.com/wiki/Map_bonus_reward/profit
Making 18g per 40 materials for a total of 210.000 Karma gives 8.5s/1000 Karma, which is better than Wintersday gifts at a decent pace of Karma-costs.
In summary, to drop a lot off karma quickly, wintersday gifts and wooden dagger are fine. Since wintersday gifts prices are low, waiting to sell until May will probably only gain around 15% profit. The bringer insignia recipe might be a better investment.
With a maximum effort using the forge for rare karma-weapons you can up to tenfold the gain, though.
A good middle course, in my opinion, is buying frostbitten gathering tools and buying pact supply materials each day.