The mobile version of Safari Web browser is not only capable, it's much better than anything built into other mobile platforms. However, it has a few limitations, the biggest of which is the lack of a real full-screen viewing mode. The implications of this are annoying, especially in landscape orientation where a great deal of the screen is taken up by the status bar on the top in the iPad version and the bottom on the iPhone.
Most of the better third-party iOS Web browsers provide a full-screen view, replacing the menu bar with small, transparent icons that let you display menus and access most common functions like page navigation, switching to other tabs, etc. The best ones even offer a way of setting the transparency factor of these icons.
Of all the alternate Web browsers available, I recommend iCab Mobile ($1.99, app2.me/2944), with Atomic Web Browser ($0.99, app2.me/2945) and iBrowse ($0.99, app2.me/2946) coming in second and third. All are available for both the iPhone/iPod touch and the iPad. If you only have an iPhone/iPod touch, you may also want to look at Opera Mini (free, app2.me/2878), especially if saving on data usage is of extreme importance to you. Let's take a look at how they compare, feature by feature.
Using tabs to switch between Web pages
Although painfully missing from Safari mobile, many third-party browsers support a tabbed display of multiple Web pages, making it easy to switch between them. iCab and Atomic Web Browser have tabbed displays, but because of the iPad's somewhat limited 256 MB of Ram, the app can crash when it runs out of memory. iCab is particularly prone to this. Atomic can be configured to display a warning when the amount of free RAM decreases to a dangerously low level (around 20 Mbytes). iBrowse and some other apps use clever memory caching tricks that reduces or eliminates crashing but only allows for sequential and somewhat delayed access to tabs.
Locking and/or restricting access to the browser
iOS devices allow users to restrict access to Safari and other features via Settings >General >Restrictions screen. This feature also lets you disable the display of apps rated 4+, 9+, 12+, or 17+ (referring to the age appropriateness rating of the app). Unfortunately, if you select 17+, you disable the display of ALL user-installed apps with that rating.
Password protection offers some security, and both iCab and Atomic Web Browser support it. In addition, iCab has a"guest mode" feature that lets others use the browsers but not have access to any of your bookmarks or your history and cookies caches.
Decreasing screen brightness when browsing at night
The minimal brightness level of the iPad can still be pretty high when you're using the device at night or in other low-light conditions. While there's no system-level solution to the problem, iCab and a few iPad Web browsers not mentioned in this article can dim the screen below the default minimum level. I hope this capability is added to future versions of iOS and to updates of the other Web browsers.
Customizing Web page text size
You can "pinch" in and out on Web pages in Safari, but you can't change the default font size of the text in a Web page (without using "scriptlets"—see the "Web Browsing Bible" at iPhoneLife.com/blog). The ability to adjust font size is available in all the browsers mention in this article, but its implementation in Atomic Web Browser is clearly the best of the bunch. This browser even remembers the text size you set for a given website so you don't have to manually switch size every time you change sites.
Searching for text in a Web page
Safari also lacks the ability to search a Web page for specific text (again, without using scriptlets, which can be hard to install). Fortunately, all of the browsers in this article include search functions. Unfortunately, only Opera Mini has support for moving to the next occurrences. This need to be corrected in future releases of the other browsers.
Reducing data and speeding up page transfer
Opera Mini is a remarkable cross-platform application in that it lets you access the Web through Opera's own server, which reformats Web pages for smaller screens and reduces the file size of the pages you access. This not only reduces data usage, it speeds up page transfer/rendering times, especially over slower connections. If this is your overriding concern—if you have a really slow (e.g., GPRS) connection or want to use as little data as possible (e.g., you're roaming abroad)—Opera Mini should probably be your first choice.
Some Web browsers (iCab and iBrowse, but not Atomic) support Google Mobilizer, which also compresses Web pages. Unfortunately, this solution can mess up page layout. If you use and are not satisfied with Google Mobilizer, you might give Opera Mini a try. Unfortunately, it doesn't support the iPad.
Safari will let you stream some videos and save images, but it does not have the ability to download and save files/documents from the Web and pass them on to other apps. For example, you can't download a PDF document from the Web and pass it on to GoodReader. Of the apps mentioned in this article, only iCab and the iPhone-only, Opera Mini let you do this.
More information on iOS Web browsers
For more information on these and other browsers, check out my post titled, "iOS Web Browsing Bible" on the iPhone Life blogs (iphonelife.com/blog). It includes a thorough comparison of all Web browsers available for the iOS platform.