Void started on Magmaw and we killed him/her/it pretty fast although I have to admit it was pretty healing intensive without "good" gear. Blackwing Descent is probably the best place to start if you're looking for a raid where you can down a few bosses without having to change instances. Magmaw and Omnotron D.S. are somewhat equal in difficulty, yet both have a different point of attention that can cause trouble. Magmaw is easy to understand but can be a bit troublesome on your healers and can go wrong quickly if you don't focus, ODS is not that healing intensive (it's the only fight so far that we two healed because we lost a healer at the start) but it might be confusing cause of the many mechanics and boss abilities that you have to be aware of.
In Bastion of Twilight you have Halfus Wyrmbreaker. Halfus is a pretty straight forward fight, the rare attribute about this fight is that it becomes easier the further you progress! At the start healers will probably have to use a cooldown or two to keep everyone save but ones all the drakes/whelps are down you can basically heal the fight with your cheap heal alone :).
In Throne of the Four Winds you have the Conclave of Wind, this fight is at the level of the Gunship in ICC ones you understand all the bosses (Rohash is sooooooooo boring to heal). The only trick here is that the loot is kind of a gamble, it drops epic gear with random enchants. While there is some BiS gear it is very very hard to get the exact piece that you need, therefore I would not recommend to start here, because the change to improve gear-wise is low.
Personally I would advice Blackwing Descent, mainly because you have two bosses that are close to each other without to much trash in between. Halfus is easier to down, but the thing with Bastion of Twilight is that every new boss is a level higher in difficulty so after downing Halfus you might be forced to go to Blackwing anyways. Conclave is only there for an extra bit of Valor Points, not much else to find there (unless you are very lucky!).
ON TO THE NEXT LEVEL!
Ones you got the first bosses down and got some upgrades across the group you might want to consider to move forward in Blackwing Descent! Void kept pushing further into Bastion of Twilight, Valiona & Theralion are not that much of a complicated fight but the following fight (Council) is a big step up the difficulty ladder, if you struggled with Vodka & Tonic than Council will give you some headaches!
In Blackwing Descent you have three bosses that are rather easy, with Atramedes being the easiest! Chimaeron looks scary but it really isn't and Maloriak is also rather simple, you just need to have some well timed interrupts. Personally I had loads on fun on these fights, because Atramedes and Chimaeron introduce some very interesting and unseen raid mechanics!
In Throne of the Four Winds you only have Al'akir left after downing the Conclave, I would leave this big lad for later! :)
So after you finished off the first few fights you can either move forward in Bastion or Twilight or Blackwing Descent! Personally I would go Blackwing, the fights there aren't "uber hard" and you will gain more upgrades for your raid than in Bastion, which helps with the progression of course!
THE LAST PUSH...
After downing 5 out of 6 in Blackwing Descent and Vodka & Tonic in Bastion of Twilight you only have Al'akir, Nefarian, Twilight Ascendant Council and Cho'gall alive! I would advice to go into Bastion of Twilight and finish Council plus Cho'gall! Cho'gall is a nice change from the rather mediocre fights in the first half of Cataclysm normal raiding tier. It needs a good awareness and understanding and teamwork of course. Al'akir is a bit like Conclave, for me killing him was only worth the achievement, I don't think Void will be going back to kill him anytime soon :). Currently we're wiping with a smile on Nefarian and from what I can tell he's the pinnacle of the first tier of Cataclysm. Keep the best for last they say... Nefarian is that bit!
Void wishes everyone the best! My guild and myself hope you all enjoy raiding as much as we do :) if you have any questions please to not hesitate and leave a comment or mail me!