That's actually a tough question for me. I'll do a top 5 instead.
Obviously I have a very big soft spot for Kyle Katarn, Rebel Operative, since I got to design the piece as a prize for winning the National Championship at Gencon 2010. It's exactly the kind of piece I like to play (very tech-focused with a ton of potential if you know how to use it right), and is in one of the factions that I love to play. Plus it has my name on the card.
The first mini I fell in love with, though, was Kyle Katarn Jedi Battlemaster, and I'm still quite fond of him even though he doesn't see as much play now as he used to. If you haven't gathered it yet, I'm a huge fan of Kyle Katarn, and he's definitely my favorite character in the EU and only really competes with Han Solo as my favorite character in all of Star Wars. Add that to another tech-y piece who can also stand toe to toe against many others and he was one of the big reasons that NR became my overall favorite factions.
At the moment I really, really like Corran Horn from Vengeance (not released yet, but his stats have been spoiled). He's another EU character that I like a lot, and his presence will help the NR break away from the Solo Charge rut they've been in for a while. I'm seriously considering playing an NR squad at Regionals this year without Mara Jade, Jedi.
The new R2P0 in NR is another recent favorite. He doesn't seem to impressive at first, but when you start building synergy around him he becomes worth far more than what you pay for him. Disruptive, Bodyguard (with Regeneration!), and Blaster Upgrade (in a faction that can potentially get a lot of use out of it if you do it right) all in one neat little package with enough HP to stick around long enough to matter.
I'll go ahead and make this an even top 5 list and say that after them, I really like GOWK. I never really played him before the SSM change, but last year I took him out a few times. I like him because he's really contrary to my normal play style, in that I normally play very tech-focused squads as opposed to brute force. I'm the guy that plays no Ugnaughts but 3 base Override characters with easy access to 2 more. GOWK is just a beat though. He's a defensive powerhouse, and has an amazing CE that doesn't give an extra shot so I can set up weird full run then shoot turns or give tempo control or swap; it just gives stats! Raw, fun, stats! I like playing him with a couple JWMs and just running up the middle to beat stuff up with high Attack and Defense values and save 11 defensive mechanics. It's really nice to take a break sometimes from crazy overthinking squads that you can't make a mistake with because everyone has 70 HP or less and hardly any defense to play with beefy dudes that don't die. He's a very forgiving piece, which is why he's my go-to piece if I want to play a casual game where I don't have to stress out over every decision. If you ask me to come up with a squad completely on the fly, odds are it will be GOWK plus a pile of other good stuff as opposed to trying to craft something too intricate.
Obviously, these aren't necessarily what I'd consider the "best" minis (although they're all quite good), since I don't think a list of "Ugnaught Demolitionist, Mouse Droid, General Dodonna, Lobot, R2-D2 Astromech Droid" is that interesting.