I typically play as a ranged character. In 1.2.4.1, I found an archer (mostly) build with the Tsunami and holy arrows to be very effective. I've modified this strategy slightly for 1.3, with the addition of the Phantasm, with its single target proficiency, and the addition of Vortex armor (with the synthesis of all 3 ranged sub-classes that were defined by Shroomite armor).
For the first few waves, you can likely remain in vortex stealth for additional DPS.
Weapons:
Phantasm (holy arrows)
Tsunami (holy arrows)
Chain gun (rapid prefix, ichor bullets) XOR S.D.M.G. (luminite bullets) Switching between ammunition types is an unnecessary pain.
Golden Shower (inflicts the ichor debuff, with the added benefit of piercing)
Stardust Dragon Staff
Stationary minions (summon these immediately before starting the event, but they may not be worth resummoning in the middle of the event):
Lunar Portal Staff (place close to the ground to make use of its piercing effects)
Rainbow Crystal Staff
Optional:
Staff of the Frost Hydra (can be difficult to obtain, and is less effective)
Queen Spider Staff (contributes little, but if you can have one, why not? Note that it definitely not worth resummoning in the middle of the event)
Weapons:
The Phantasm will primarily be used for its high single-target DPS. I would reserve this for Everscreams, Santa NK-1s, and Ice Queens.
The Tsunami is excellent for crowds, but perhaps not significantly better than the Phantasm (especially when yetis start to show up). Alternatively, the S.D.M.G. with luminite bullets will also perform well for crowds.
The precision of the S.D.M.G. can be a bit of a disadvantage when all you need to do is inflict the ichor debuff. (The gun is more precise than the accuracy of the user aiming it allows.) This is where the higher fire rate and spread of the Chain gun is advantageous. If you do not need to use a gun for crowd control, the Chain gun with ichor bullets is a helpful addition.
The Golden Shower also inflicts the ichor debuff, and pierces. The range can sometimes be an issue, however. The Chain gun is more effective in such instances.
Weapons Summary:
Primary weapons: Tsunami and/or S.D.M.G.
Inflict ichor (especially for Santa NK-1 and other bosses): Chain gun and Golden Shower
For bosses: Phantasm
Accessories:
Since the [legit] Christmas event has recently ended, you may have obtained a hand warmer from one of the presents. The immunity to frozen is helpful once ice queens start showing up, but is definitely not absolutely necessary.
Magic quiver
Sniper scope
Destroyer Emblem
And 2 of those listed below:
Ranger emblem
Ankh Shield
Celestial Shell
Wings (Most use either the Vortex Booster or Solar Wings)
I would use the Cosmic Car Key (if you do not have wings, be careful, since the frozen debuff from frost waves will remove you from the mount and cause you to fall, perhaps to your death) or the Shrimpy Truffle mount (if you have a hardmode expert world). If you have the means and patience to make a flooded arena (remember to make air pockets for camp fires and heart lanterns) then I'd recommend doing so for the great speed (and damage) boost provided by the submerged fishron mount. If not, you can still get some of the benefits by making small water pockets contained in bubbles. The Cute Fishron mount in water outperforms wings in terms of its horizontal movement boost, so if you take this route, wings will definitely not be necessary, as the sheer speed of the fishron mount makes dodging quite easy.
Very helpful buffs to obtain: (You definitely do not need all of these, so I'll organize the most essential ones at the top)
Warmth potions (Requires fishing, but definitely worth it.)
Lifeforce potions (Requires fishing, but definitely worth it.)
Endurance potions (Requires fishing, but definitely worth it.)
Ironskin potions (Although not as effective as the endurance potion, it is easier to obtain. Having both would be ideal.)
Regeneration potions (easy to obtain)
Any food item for the well-fed buff. (Pumpkin pies are great, but the entire event lasts no longer than 9 minutes, and you may die before the full 9 minutes ends. If you end up fishing to make some of the other buffs mentioned, you'll likely end up with many ingredients for cooked fish and/or sashimi.)
Rage potions (if you have access to a corrupted world, wrath potions are also very helpful.)
Archery potions
Optional:
Magic power potions (if you do go with the build I suggested, magic will form a very small portion of your DPS)
Swiftness potions (these do NOT affect the speed of mounts)
Heartreach potions
Summoning potions
After doing the event "countless" times, I would hope that you have obtained at least a few banners. Place identical banners 196 feet away from one another in the horizontal direction for continuous coverage and efficiency. (Try grappling to the block that the banner is attached to in order to get a good GPS reading.)
The same distance of 196 feet is used for the heart lantern, star in a bottle, and camp fires. However, at your point in the game, you should have the resources to make enough of those that efficiency is not a major concern.