Ranked in these QuestionsQuestion Ranking
Pro AdBlocker onboard
It's possible to add own filter lists. The internal adblocker is faster than any external.
Pro Video pop-out feature.
You can pop-out any video and it will stay on top while you are surfing on other tabs.
Pro Compatible with Chrome extensions
Since Opera is built on WebKit, the same engine Chrome (among other browsers) is built on, it was possible for Opera developers to allow Chrome extensions to run in their browser.
Pro VPN onboard
Free and fast VPN onboard, includes Germany, Canada, USA, Netherlands, Singapore.
Pro Strong HTML5 feature support
Opera scores highly on HTML5 feature support.
Pro Free and open source
Pro Opera turbo
Opera has a functionality called Turbo which increases browsers speed and reduces data consumption considerably by compressing the data that's found in a web page.
Pro Battery saving mode
Opera is full of user controlled settings. Everything can be imported and exported even RSS feeds. It can be skinned in a variety of different themes or it can be extended through the use of a large number of plugins available.
Pro You can install extensions on the sidebar
Unlike other browsers, you can install add-ons such as tabs, bookmarks, history, sessions, notes, and extension manager in the sidebar. So you have the flexibility to use it for your purpose.
Con Original version using Presto engine is dead
Current version is built on WebKit/Blink, which means it shares cons of Chromium: high RAM usage, lack of customizability.
Con Uneditable default search providers
It can not delete or replace already built-in search services such as Yahoo, Google, DuckDuckGo, and Wikipedia.
Con Fewer extensions
While Opera is currently available gratis (without monetary charge), it is currently not libre (meaning that it does not allow users to view the source code used to create, to modify that code, or to redistribute modifications) and is therefor neither free nor open-source software.