having used both bigbluebutton (bbb)0.81-beta and open meetings(om) version 2.0 in real time online courses I think I have some experiences on both of them. First of all, afaik, om has plugin only for 2.2 verion of moodle; correct me if I'm wrong. The moodle plugin of om for 2.2 version migth work in moodle 2.4, but I haven't tried it personally. Finally, the followings and comments might contain some invalid information especially due to the versions of the both video conferencing tools and my personal lack of knowledge. So please feel free to correct the areas you see any incorrect information. You can give a trial shot for bbb here and om here.
Anyway, here are the areas I'll compare them:
1- Chat module:
In bbb chat module is vertically placed on the right by defaults, which give you the opportunity to view nearly all the messages from the participants. In om, however, it is placed horizontally in a rectangular box just beneath the whiteboard in which you can see the very few messages from the participants even if you hide the admin panel
Prior to 0.81 version, bbb was showing certain characters of the participants' names (such as Grah.. instead of full name Graham Stone). But in 0.81 beta version this was corrected and full name of the participants can be seen.
Again prior to 0.81 version of bbb, you could change the font color of your messages. This was a very good feature especially in discriminating the messages. However, in 0.81 version you have only one color: black. I believe this will be corrected since 0.81 version is still in beta
In bbb there is also a private message area in which you can send private messages to the users similar to adobe connect. I say similar because in adobe connect the teacher is informed if a participant sends a private message to the other. In bbb, teacher is not informed if any of the users are privately chatting unless the recipient is the teacher himself. In om, afaik there is not a private chat feature available.
2- Users block:
In om, users are given more permissions such as turning on their mic even if you disable them to avoid echo. bbb is more aggressive than om in this aspect: Once the moderator logs in and set turn off all mics, every new comer enters the conference as their mics off. This is a good feature to avoid echo since every user does not use a headset with mic. And in om, if you choose webinar as conference type, the mics can be bulk turned off. But this time, if you want to allow a participant to speak, you have to first click on the user's name then click again to turn on his/her mic, which requires a double click to turn on and double click to turn off. This might cause problems if you have a crowded class.
The tools in om is undoubtedly richer than the ones in bbb; especially the icons and type tool. In bbb 0.81 beta version type tool is added, through which you can type on the whiteboard. However, the typed items cannot be dragged to another place as it can be done in om.
In om you have one useful too, which is polls, through which you can create polls (let's say questions) and ask the participants to make their choices when they are ready. At the end of the voting session a pie chart is shown.
4- Uploaded materials:
The materials uploaded by the teacher in om remains in teacher's account even if s/he logs out the conference and backs to moodle. In bbb, however, once the teacher logs out and logs in again, s/he has to upload the materials again to use them.
In om, you can have more than one whiteboards whereas is in bbb you can use only one whiteboard.
In om, you can record the session with the editing tools. I mean if you draw something on the whiteboard, it is recorded as well. However, in bbb the things that you draw on the whiteboard is not shown in the recording; only the slides and the voice of the teacher. I think this is because of the format of the recording. The slides are saved as .swf files and audio as .vaw. And they are saved separately. Another point to consider is if you have sessions one after another, you should think about the recording process one more time. I mean while the recording of the older session takes place, another live session will tried to be handled by the server: How a powerful server you have, you should think about the server load.
In om, you can also define which areas of the screen to record. By this way you can record let's say the video view of the teacher. In bbb, however, only the whiteboard and chat module is recorded.
As a solution, you can think about using a screen capture program. Besides commercial ones if you have a Ubuntu machine you should give a try to kazaam, which gives very good quality output with a small file size.
You can install both moodle and om on the same server since om runs on port 5080 while moodle runs on port 80. But personally I do not recommend running the lms and video conferencing tool on the same server, especially for production sites with large amount of participants. But if you have a small number of participants and budget, this can be considered. Although there are some attempts to run bbb on a different port apart from 80, (personally I tried it too) it stopped working after a successful 30 seconds runtime.
BBB developer Fred Dixon is very decisive on this matter; bbb requires a dedicated server and has to be run on port 80 (see here). From a technical aspect, from the outputs of our bbb server, I can say that bbb heavily relies on the processor rather than RAM of the server.
You can install bbb on a Ubuntu 10.04 server easily, and you might have problems if you want to install it on a 12.04 Ubuntu server. See here for installation instructions.
You can install om on Ubuntu 12.04 and even on Ubuntu 12.10 server. See here for installation instructions
bbb 0.81 beta version is added a new feature through which you can change the layout automatically with one click. The options are video chat, meeting, webinar, lecture assistant and lecture.
You can use om more than a web conferencing tool. I mean you can create different sessions, calendar events, user account assignments through the om portal itself. In bbb, you do not have much choice but just using video conferencing features.
Since we have been using moodle 2.5 and horizontal chat module is extremely important for us (we are using it in a language course and we frequently ask participants to share their replies/comments with us) we went back to using bbb. One more thing to add is that, personally I think, the speed of these videoconferencing tools mostly depends on the bandwidth of the server and the participants' rather than the architecture on which they are built. Best regards