When I was trying to put together the first 10 on 30b, I noticed certain figures seemed easier than others
Luke Bespin is probably the most notable for toughness on the 30b. I know of 3...though to emphasise, that's just to my knowledge, which is anything but extensive and certainly not to be taken as an absolute fact. It's possibly the toughest of the 10 to get on 30b and considerably tougher than the 30a
Leia on 30b - Not sure on this one. I always thought that the a and b versions were similar in toughnes, though others have said the b is much tougher.
Han Hoth and HRS I actually found particularly tough. Saw loads of 30a before I finally found 30b's for each character.
Lando - I have no idea. Picked up the b by chance and was not actively looking for him like I was for the above two
The remaining 5 are the tougher five so are hard pieces to find either a or b, so really hard to judge.
I think there are more b's floating around for Bossk (the first one I had was a b, which I sold when I got an a). I've only seen two bossks come up for public sale since 2005 (one Vectis and one eBay) and both were 30b. I know the vectis one has passed through the hands of several collectors. I have the eBay one.
I've only ever seen two IG88's come up for public sale, both Vectis and both were 30b. IG88 was also the last 30b I needed to complete that run.
Really not sure on WBG. I did think b was more common, but several new ones have turned up and I'm not sure which version they have been.
Same with the HST.
FX7 is also tricky to judge as so many have sold, but I think a lot have been the same figure passing from collector to collector, which can distort figures a bit. I did have 3 at one point and two of those were a. Can't remember what the recent vectis ones were.
Not sure if any of that helps much as like I said, it's just my experience. I stopped looking in 2010 and a lot has changed since then.
In terms of impact on price, logic would suggest that a would be more than b. A is the debut card and in general this is what most collectors go for. Consequently there would be more people going for an a rather than a b so greater demand = greater price, irrespective of rarity. That said in some cases people would be just glad to get any version of the card, so they are still hotly fought over. This would be true of the tougher ones.
Luke and Leia are the odd exception. They both have a different card design, whereas all the others just have a different logo size. If this is appealing to variant collectors then, if the cards are truly rare (as is definitely the case with the Luke) that could swing value in favour of the b. However I've seen a sell for far more than b in the case of Luke many times. So who knows!
I clearly don't