I thought I'd never return to Magic after selling my physical collection some months ago, but Arena got its hooks in me and dragged me right back in. I started out with just a standard Izzet Drakes list, but WAR didn't really bring anything new to that deck so I started building some of my own. I'm especially loving Boros Feather and Orzhov Aristocrats so far;
Feather can be very explosive with Dreadhorde Arcanist and Tenth District Legionnaire - T2 Arcanist, T3 Legionnaire + Gird, then attack and cast Gird again with Arcanist and you've got 9 power on the board heading straight for your opponent. Gideon is extremely useful and should not be underestimated; granting Lifelink to a big Legionnaire can swing games against aggressive decks in your favor, granting Indestructible to Arcanist allows you to safely trigger its ability against what would otherwise be a lethal blocker, granting Vigilance to another creature allows you to be aggressive while still protecting Gideon from a counter-swing, he's an Indestructible 4/4 Creature on your turn, and sometimes you can just -6 him to get rid of something. If you get Feather to stick, you get to recycle all of your removal, card selection, card draw, and protection every turn. I might play around a bit with the exact distribution of non-creature spells, but I've been having a blast so far with the current list.
Orzhov Aristocrats is very satisfying to play. Priest of the Forgotten Gods is just so good - it gets rid of a Creature, hits your opponent, triggers all your death triggers, draws a card, and ramps you. It enables a T4 Liliana and can protect a T6 Liliana from Spell Pierce. Bankrupt in Blood is also great. Just two mana to sacrifice two fodder creatures for three cards is already good, doing it for five cards (with Liliana) is amazing, and doing it for seven cards (with Liliana and Teysa) is absolutely ridiculous. Sorin and Ajani are there to bring stuff back from the graveyard. Sorin can instantly -4 to bring back Teysa if needed, while Ajani can just sit there and tick up if you're ahead. The Militia Buglers were a late addition, but they've worked out well so far. They can fetch any creature from the deck and if need be you can bring one back from the graveyard with Sorin to dig for a Celebrant or Teysa. Spark Harvest is cheap removal that targets both Creatures and Planeswalkers, backed up by two Mortify for Instant-speed removal and Enchantment destruction. Cruel Celebrant just sits on your board and wins you the game.
I've also been trying to work out a Selesnya Proliferate list but haven't been able to get it to the place I want it to be yet, and I'm tempted to try my hand at a Mardu variant of Aristrocrats if I can gather some more Rare Wildcards for lands and Judith.