After having maxed out most Rebellion SB reward cards, I wanted to update my original RB SB reward card tier list to help some newer players, as well as those who haven't completed their collections, decide which reward cards they want to max out first.
Here's the new one, along with arrows show up-steps and down-steps (explanations below for cards that I've moved):
Arachne Weaver (S ==> S+)
I moved this one up to S+ tier. Although you might look at this and say it's not quite as dominant as Olivia, I would argue it is in many cases, and also provides utility in many different rulesets. The main draw here is obviously the Corrupted Healing, though its other skills (Scavenger and Poison) also provide a ton of utility. Looking at card usage stats, it's clear it's an S+ card.
Halfling Refugee (A ==> S)
Absolutely a S tier card due to the 1 mana, neutral splinter, and 5 (five!) damage. I use this card ALL the time.
Ujurak Elder (B ==> A)
This one I already had pretty high (at B) but moved it up to A. It's very versatile, provides a ton of team utility with Strengthen and Swiftness, and is more survivable than it initially looks thanks to the Divine Shield. At 3 mana and being neutral, it's therefore super versatile.
Shock Trooper (B ==> A)
Although it has a horrible debilitation, the 5 magic damage for 4 mana is insane. You can also consider using it as a tank to fire off one hit and die in an early round if you want to prevent the zapping. In back-to-basics it's one of the top cards in the game (along with Halfling Refugee).
Chaos Evoker (C ==> B)
I moved this one up because 2 magic damage with Ambush and Blast pairs extremely well with Lorkus, so I find myself using this one successfully a lot.
Nimbledook Explorer (S ==> B)
I originally had this one at an S-tier, but the availability of other no-attack cards in the Light splinter and prevalence of corrosive ward and Venka make it a rare choice for me. Maybe I just haven't yet quite found his spots.
Surly Drunk (A ==> B)
He's the best of the 1-mana legendaries, but not an A tier card IMO. Bumped to B.
Death Ranger (A ==> B)
This card's quite sturdy with the void armor and 7 armor, but it just doesn't come up often. Scavenger's a great ability but it's weird on this card. Hard to place it consistently.
Giant Alpine Skink (B ==> C)
With the number of great front-line tanks in Water, I don't find myself going for this guy often. However, it may be an option once Djinn Oshannus leaves Modern due to phase (as an alternate to Slade with the card that gives phase), so it may make a resurgence.
Drybone Megalodon (B ==> C)
Interesting to have this one in Fire, where there are two other flank cards with attacks. As a result I don't find myself going to the Megalodon often, as I think Flank is one of the primary draws.
Warborn Chieftain (-1 ==> C)
AKA the Chieftain who can't quite figure out what he wants to be when he grows up. Are you anti-melee? Are you anti-magic? What's phase doing on a 3-speed card anyways? Why stun when you're a tank?
Halaran Huntress (B ==> C)
Mini-Venka just doesn't really do it most of the time. Possibly because she's a melee card in Earth where Tofu dominates and doesn't provide much utility in that meta.
Sergeant Grauzral (B ==> C)
3 damage just isn't enough for this card to get regular usage. Nid likes Blast cards, and this one has opportunity so you could imagine him getting some air time there, but usually it just doesn't work out.
Blackmoor Wild Elf (C ==> D/F)
For 5 mana, this card's stats just don't deliver. There just isn't enough use for a cripple card that hides and gives amplify. Anywhere.
Skyspire Leopard (C ==> D/F)
Bad kitty. Real bad.
Quilliun Legionary (C ==> D/F)
This guy's in the same group as the Chieftain, i.e. it's not sure what it wants to be. Anti melee? Anti magic? Void makes no sense in this kit. 2 Ranged damage also doesn't do much, and even if it gets a Bloodlust or two, so what? would 4 ranged damage really make a difference? If the Void was a Piercing, maybe. But with this kit, there's just way better choices for 8 mana.
Card usage tools for reference on how much these (and other) cards get used: