There are a lot of IDE used for RoR development like RadRails NetBeans TextMate JEdit
but i would like to know which one is the most widely used , and could be recommended ?
There isn't "the most efficient IDE". What it counts is what you feel most confortable in. I like NetBeans 6 very much, probably would have tried TextMate if it was available on linux. Try them for a short time then use whatever you like the most.
Add my vote for Aptana RadRails. It's java based so it works on multiple platforms and the Aptana team has been making big strides in its development. I really like it now more than ever.
I checked out with Aptana and it needs to register for a trial version, how i wish there's a free IDE with intellisense feature like Netbeans maybe.
I'd go for Aptana Studio from http://www.aptana.com. It's a a java app, so i use it on both Windows and Linux machines. I use Subclipse, which is intergrated for versioning via SVN. Although it is an IDE it is not one of this big bloated IDEs if you configure Perspectives to your private needs.
To recall your question: I don't know about efficiency - it's fun to work with - efficiency starts in Rails by script\generate'ing models, controllers, scaffolds, etc. Just my $0.02.
Netbeans 6.0 will do. Just need to tweak things specially when you are running Linux/OsX system. Not that major tweak but will help a lot. Netbeans do have a complete documentation for it. If you are running MAC use TextMate. It's as powerful as Netbeans but less resource needed.
One thing i like about Netbeans is the Format-CODES.
I use RadRails v0.7.2 , it uses a lot of system resource and most of the time i end up with a Not Responding Message ,but this could be because i use to have lot of files openend in the editor at a time or because of my systems hardware limitation , well i am planning to upgrade my radrails version soon.
i think it's not the rad rails version. it's the jvm that is eating all the resources. try unloading some projects. to prevent the IDE to index the project.