General

Firefox (nightly at least) recovers tabs when the browser crashes, if this ever even happens. Only the active tab is reloaded, ensuring maximum speed. Other tabs are loaded when they become the active tab. This allows the smallest possible wait to get back to browsing instead of a lag spike it would get if all loaded at once.

Firefox/Nightly is ridiculously better at managing large amounts of tabs than Chrome or Chromium.

Other recently added Nightly features include per-window private browsing, many under the hood speed improvements, and near perfect image scaling.

By default Nightly uses the same profile, therefore any settings you may have on Firefox stable would transfer to nightly and vice versa. Just remember that anything you dislike, you can manually change either by editing settings or with addons. An example of this is the download management.

I personally dislike both the old and the new download management in firefox and nightly. To correct this I use an addon called All In One Sidebar, which I set to 0px length when collapsed so it is not present at all. I open it with F4 whenever I need to do anything such as manage addons, downloads, etc.
Then I go into about:config, and search for 'browser.download.useToolkitUI' and set it to TRUE. This disables the new 'bubble' download method which gives my sidebar proper functionality again, making downloads completely unobtrusive. This one of an infinite amount of scenarios where you can fix firefox/nightly the way you want it whereas chrome/chromium would have no solution due to its closed nature.

I don't know if this is a good reason (or if it even makes sense), but I usually have 30-40 tabs open and since Chrome handles each tab as a process, stability seems to be more guaranteed than if Firefox were to handle that many tabs (I haven't used Firefox in 2+ years so I don't really know their new features). I have Firefox installed because there is an extension for the browser that lets me download Youtube videos and videos on other pages (Google's Chrome specifically does not allow extensions to download their Youtube videos). Because of Chrome's omnibox (which is really stupid--there's no option for the user to control what the omnibox displays, so it will display your history, bookmarks, etc., whereas on Firefox, the user is given the option to prevent the address bar from recommending anything for privacy concerns), I plan on syncing personal bookmarks and dealing with personal data on Firefox and doing everyday browsing on Chrome.

I will try both Nightly and and Chromium. I hope a Chromium user can give me more insight on the stability of Chromium and whether checking Chromium's download site every day is the only way to keep the browser up to date.

Yes, it is a known fact that Google Chrome is a very unwise choice for privacy reasons alone. Chromium is a pre-release (I am unsure which stage of pre-release) which does not yet contain most of stable release's tracking features.

However why use chrome? Why not use Nightly (Firefox nightly alpha build) instead? Much, much more potential for changing it to your liking. Here is mine. It's quite simple, but very many different styles can be achieved with the right code.
http://i.imgur.com/BSAmz.jpg
It's not too difficult to work with style scripts for firefox based browsers, and it is in its nature to be able to be edited to any way one desires. However this is merely half of it. I have many scripts and changes to the internal workings of it both via the config files and about:config. I don't understand why anyone would use Chromium when nightly offers much more: pretty much all of chromium's features (or better ones) and at faster speeds. The one and only drawback is lack of support for the most obscure media formats which are never used, so it's not really a drawback.

As for stability, it's just as stable as Firefox stable for the most part. Think of it like Debian Wheezy. It's technically unstable by name, but it's stable as a rock. I've had like one crash with nightly, ever, and I've rarely heard of anyone having any sort of crashes on nightly that were not something that would have happened on stable anyways. As for speed, it is as fast (or faster) as any other major browser currently available. As for customizability, it's leagues ahead of any version of Chrome, and equal to or greater than Opera, as all the same things can be achieved (just not always in the exact same ways). As for content, it is miles ahead of both Firefox stable and Chrome stable, and a fair bit ahead of Chromium.

NOTE: By default nightly has a few settings that relay purely hardware / performance information to Mozilla in order to help with the testing effort and prepare an Aurora release, however all of these features can be turned off easily in the options if you wish to remain completely private. Furthermore you should enable Firefox's "tell websites I don't want to be tracked"

Edit: On topic, yes Chromium is much better than Chrome stable. You can get the latest build in their FTP servers I'm pretty sure. It may be a bit more difficult if you use Linux or BSD, but if you use Windows it should have a straightforward installer.

For privacy issue:
Google collect data on all user searches and web site visits to supposedly improve their search and delivery more effective ads.
If you are concerned over what google have collected and if you have a google account then login to it and clear your search history, then delete/cancel the account. Also clear all your cookies and local search history from the browser everyday just before turning the computer off.
There is nothing you can do if google tracks search history by IP.

For security issue:
Make sure you have anti-virus and anti spyware detector/scanner installed and have their definition updated and a full system scan at least once per week.
Configure your computer to create daily system restore points on bootup or sometime during the day.
Set up a access policy so that only the legit programs (i.e programs installed into c:/program files as an example) only can be executed, to help prevent some of the nasty single click web base viruses from inflecting your computer.

* Hi Hi Ky Ky *

[quote=Rationale]I swear someone asked this before. I thought chromium was just the testing version of chrome anyway?[/quote]

That leads me to another question: is Chromium stable enough for the average extensive internet user? From what I know, there is no stable build.

I don't think it's too difficult to understand that humans crave a certain level of privacy and security--that's why doors, locks, methods of encryption, passwords, etc. exist. The internet is such an open space where data is shared and accessed by everyone and I want to know the ways of maximizing privacy and security at a practical level to protect my identity. I want to know who has access to certain data and what they intend to do with it.

i use internet explorer.