I also have all 5, so here are the pros and cons:
IM2 - My very first HT figure. Surprisingly few accessories. Very limited posability mostly due to the suit. To date, this is the only one with ankle articulation, but it also renders it susceptible to leaning forward and fall over. Great for static glamour poses, don't bother trying any dynamic action poses. The face is nicely painted but not as good as the prototype. The rooted hair was okay, but HT was still pretty inexperienced with that at that point. The tallest of the five as the body is still based on the generic body.
Avengers - A clear improvement over IM2. The new smaller body makes her fit better with the team scale wise. To date, this is the only one with throwing discs, which she never actually use in the final film. Started the trend of no ankle articulation and the inclusion of "lighted up" wrist gauntlets on this one. The rubber suit works much better than the IM2 version and this one is good for both static and dynamic poses. It gives the best booty and silhouette. The face is closer to the prototype, it is very nice but I cannot call this a good rendition of ScarJo. She is good looking, but not ScarJo. The hair is more manageable on this one. This one has way more accessories comparing to the puny set available with IM2 version. Overall, this is a huge improvement over IM2 and sets the tone for all subsequent BW releases.
Winter Soldier - The cloth suit created unexpected difficulties in posing her and they included accessories that have little use in posing her (a cellphone?) I would have preferred a pipe wrench or something else. The head sculpt is an improvement over Avengers where I can see the resemblance to ScarJo better, but still not the best likeness. The hair again is pretty good straight out of the box. An improvement over the likeness but went backwards on accessories and overall articulation.
Age of Ultron - The suit is certainly flashy and the cutting is better than TWS, as a result, articulation-wise is an improvement over TWS. The head sculpt is the same as TWS with a repaint, which to me is okay, but the rooted hair is a disaster on this one. It looks nothing like her hairstyle in the movie and it looks like a mess no matter what. In terms of accessories, this one takes the cake, you get 2 giant Hydra/Chitauri rifles from a deleted scene from the trailer and both extended and retracted batons on top on her pistol and gauntlets, plus energy effect parts! However, there is no place to put her retracted batons on her belt. Overall, a very good release, loves all the accessories, but they went way backwards on the rooted hair. Best value to date.
Civil War - By now, it is starting to get pretty boring collecting BW and HT is aware of this as well. So they up the ante by giving this one the best head sculpt yet! The resemblance to me is stunning! The rooted hair is far better that AOU and the suit is much closer to TWS in terms of cutting, so a result, we get a bit of a ding on articulation. The accessories are fewer again this time (2 sets of batons + mini Ant-Man plus the usual), but you can put the retracted batons on her belt at her lower back.
Overall score (0 - 5, 5 being the best)
IM2: 2.0 (I think it deserves a ver. 2.0)
Avengers: 3.8
TWS: 4.0
AOU: 3.7
CW: 4.2
Dubious Awards:
Coolest accessory: Throwing discs and disc throwing hand - Avengers
Most pointless accessories: Cellphone - TWS, Dagger - AOU, Ant-Man - CW
Best a$$ - Avengers
Best face - CW
Best hair (straight out of the box) - TWS
Best box picture - AOU (such a bada$$ picture of her)
Biggest deviation from prototype - IM2 (face), AOU (hair)
Best value (at release) - AOU (most accessories)
Most fun - Avengers (All subsequent releases are basically variations of this one)
Roads not taken:
Civilian clothing Widows from TWS & CW
Arctic Widow - White suit (with CW suit)
Wishful thinking accessories:
IM2 - everything she actually used
Avengers - Loki's scepter
TWS - pipe wrench
AOU - Cap's shield
CW - none