The two biggest players in the Drupal 7 webshop field are Drupal Commerce (also known as DC1) and Übercart . DC1 actually started as an Übercart rewrite to make use of Drupal 7 APIs. After the split Übercart was ported to Drupal 7 too but it was still using Drupal 6 technologies.
Although still very much in development, it seems something similar will be true for Drupal 8 as well. The developers of DC2 (the Drupal 8 version of Drupal Commerce), lead by Bojan Živanović rewrote the whole system from scratch to make use of the huge changes in Drupal 8. They are active members of the Drupal developer community so they not only know but also form the actual best practices. While working on DC2 they have fixed many dozens of Drupal 8 core issues and much more in other contributed modules (such asEntity, Inline Entity Form , Profile ).
A great realisation when rewriting Commerce was that several components of a webshop could be reused by other (not even necessarily webshop or Drupal) systems. Some typical examples are address formats, currencies and taxes. These components are usually a huge pain to maintain because of the small differences from country to country. So they have created standalone PHP libraries usually using authorative third party datasets such as CLDR for currency or Google’s dataset for address formats. Some of them are already used by other webshop solutions like Foxycart and developers even outside the Drupal community are giving feedback which makes maintaining them easier.
In the DC2 development process UI and UX has got a big emphasis already from the beginning. Based on research of existing webshop solutions the shop administration and checkout process has been redesigned by UX specialists. For example, the product creation process is quite confusing in DC1 and there’s not even a recommended way to do it. In DC2 this happens now in one single form which makes it super easy.
A new concept in DC2 is Stores. Stores represent billing locations and products can belong to one ore more stores. One use case is the need for different billing for customers from different countries. Another one is having a shop where sellers can open an account and sell their own products. In this case each seller has their own store.
There are many other new features and improvements like a new and flexible tax system (you can say things like: “from Jan 1st 2014 the VAT changes from 21% to 19%”), a redesigned checkout flow, different workflows for different order types etc.
DC2 is still in alpha phase and is not recommended for production use yet. Beta releases will already have upgrade paths between them and so can be considered for starting real sites with. Beta1 is expected for May.
Drupal Commerce is the most popular e-commerce solution for Drupal 7. Given the high quality code and responsiveness to developer, shop maintainer and customer needs I do not expect this to change in Drupal 8 either.