We’ll go in reverse order, starting with Ardent Plea at #10:
Also, Ardent Plea is also one of the best Exalted cards around, as it also has Cascade. The way that the Cascade mechanic works is that when you cast a spell with it, you reveal cards from the top of your library from the game until you hit a non-land card that costs less, in this case, 0, 1, or 2 mana to play. You may cast that card without paying its mana cost. Then every other card you removed from your library goes to the bottom of your library in a random order. Two of the best Exalted creatures of all time are Noble Hierarch and Qasali Pridemage, highly playable cards. Hierarch costs one mana and Pridemage costs two. It’s very likely you’ll hit one of those two cards with this card’s Cascade trigger.
Because of the Exalted deck’s casual appeal, as well as fair amount of play-ability with cards like Cathedral of War and Sublime Archangel that were printed in the Magic 2013 Core Set, Ardent Plea is a very nice cog in that sort of deck.
But the Coatl’s main home today is in Commander decks. Because of all the ways that counters can be used and abused that have been printed since Alara Reborn, the Coatl’s counters can be used in many different ways. Due to reprints, however, he's no longer as valuable price-wise. He was around $2 before a reprint in the Elspeth vs Kiora Duel Deck. His price dropped further with yet another reprint in Modern Masters 2015. Still, if you can draw a lot of cards and give him a lot of counters, he gets quite silly. Heck, his effect can be so abused that Star City Games even offered a Legacy decklist featuring the Coatl in 2009.
Put on the right creature, Mage Slayer can deal quite a bit of damage without a creature ever actually having to connect for damage. While it’s not the more popular of the two Equipments on the list, it is the one that can potentially deal more damage.
As much as I personally love the mill deck, and it is actually an interesting strategy that’s been making more of a push in the Modern format, Mind Funeral is a bit inconsistent in that it could potentially hit 4 straight lands. Cards such as Archive Trap, Breaking // Entering, and Glimpse the Unthinkable are more reliable as far as dumping cards in the graveyard. However, many Modern Mill lists are still finding room for at least two copies of Mind Funeral as played correctly, they are still very potent mill cards. In any case, it’s perhaps currently the most valuable and widely played uncommon from Alara Reborn, besides the number #1 card on this list…
A card that is so often played in Eternal Formats is obviously good for a reason. For only 2 mana, you pump your own creatures by +1/+1 and creatures your opponents control get -1/-1. Most often you’ll be playing this after blockers have been declared and the potential blow-out can essentially win you the game. It’s a very powerful card, and if it hadn’t been reprinted in both the Sorin vs Tibalt Duel Deck and the ill-fated Modern Event Deck, it would have a much higher dollar value.
He’s played heavily in every Eternal format: Modern, Legacy, and Commander (heck, even Vintage!) A 2/2 creature with all of that on it is pretty special, and even his Exalted ability is relevant due to the fact that he’s typically played alongside his Exalted brethren, Noble Hierarch. He’s a very splash-able, main-deck-able creature, and he’s only a common! He was reprinted in the Ajani vs Nicol Bolas duel deck, as well as a Friday Night Magic promotional version.
I don’t think the #1 card on this list can be a surprise, as format-defining as this little Elf has been…
Bloodbraid Elf is the number #1 non-rare in the set for a great many reasons. She costs 2RG which sounds a bit pricey for a 3/2 with Haste, but it’s her Cascade ability that is so vital to her success. Pretty much every card you would want to hit with her in Jund: Fulminator Mage, Kitchen Finks, among others, was three or fewer mana. She was two cards for the price of one, and heck, most of the time hitting a Terminate or Thoughtseize wasn’t the worst thing in the world, either. As someone who played a ton of Jund and Naya back in my online Magic Workstation days, I fell in love with this card. The Steve Argyle alternate art on the Friday Night Magic promo (also displayed on the Planechase reprint) made me love her more.
In 2013, she was banned in Modern, due to the fact that she could Cascade into Liliana of the Veil among other ridiculously powerful cards such as Tarmogoyf and Dark Confidant. This still happens, of course, in Legacy Jund. But the more powerful interaction is with Shardless Agent, a card that’s only ever been printed in a Planechase product.
So there you have it, the top 10 commons and uncommons of Alara Reborn. Yes, you could argue that some of the cards could have ranked higher or lower, but all ten cards deserve to be on the list.