In response to Andy's article and some comments on it by The Antipope, I thought I'd wade in with why I think that Space Marines are the ideal beginner's army...
Orks can but they're not very good at it so they are better off running during the Shooting Phase. Marines, however, are very good at shooting. Why does this matter to a beginner? Well, shooitng is lot more stragihtforward than assault. There's no "who's attacking who?", "who is actually in combat?", "what initiative step are we at?" confusion. It's simply all of these guys are shooting at all of those guys.
Basic Marines are good in Assault. They're not awesome by any means (which is the first lesson you need to learn about Marine - when to commit your basic troops into a fight) This is what makes them better than Orks though, we don't really want them in Assault whereas Orks have to get into Assault. Now, one of the hardest things as a beginner is to judge Assault ranges and to ensure that all of your Squad get into combat.
There are so many build options in the Space Marine Codex and there's probably only one "bad" unit (sorry Andy the TFC isn't much cop) You can go assaulty with Thunder Hammer/Storm Shield Terminators. You can go shooty with Land Speeder Typhoons and Autocannon Dreadnoughts But, best of all you can go balanced. You have ways of dealing with any threat within the game at range, in midfield and in combat. Orks, on the other hand have several bad units and the only good shooty unit they have (Lootas) need luck to be really effective. There seems to be one really competitive build in the Ork book - Couple of Battlewagons, Lootas and Buggies but just moving everything forwrd must get boring after a while.
Value For Money
The Marines are an elite army and by their nature will have very few models. This means that it's cheaper to but a full army compared to getting tonnes and tonnes of Boyz. Plus, since nearly all of the units are good there's no danger of wasting money on things that will be rubbish in the game.
Andy talked about how the Orks were easy to play since you roll lots of dice compared to Marines and so a few bad rolls shouldn't really affect your game. Yes, it's true that with Marines, a few unlucky rolls for armour saves can ruin your day since you can have a small army to start with, you balance this out with always requiring lower rolls to hit, to would and you actually get a save. With average rolls on both sides you'll come out on top with Marines just because you ahve better stats (note this is one of those wild internet statements with no evidence to back it up. It feels right though doesn't it?)
And They Shall Know No Fear
The singular best rule for Marines in the game. Automatica re-grouping even if veneath 50%. Plus you get base Leadership 8 anyway (9 on Sergeants) so you're not going to be running away that often anyay. Sure it takes a lot of firepower to get a Boyz Mob below 10 (especially from 30) but once you've done it, it's bye bye Orks.
AKA the reason we didn't mention Vulkan. Okay, so these are really for the beginer as they take some skill to use but I thought I'd mention them since the rule is pretty awesome. You can volntary fail any Leadership test you are called on to make. This stops pretty much any army from shooting you before Assault as you can fail and (hopefully) move out of Assault range. It means you can Rapid Fire an Ork squad, take the charge, lose the comabt, slip out the back and then Rapid Fire them again next turn. Andy claimed that 10 Marines wouldn't stand a chance against 30 Boys but I think that even at 12", Marine player going first they would (again, this is rather spurious, based on no evidence and it doesn't feel quite as right as my last claim. The Marines would take a lot of Orks with them though)
Mitigating what I said above about the Orks being boring is the fact that they do have a lot of "funny" units. Space Marine Devastators don't have to worry about how many shot they're going to fire next turn, they always know. The random nature of the Orks can make them exciting to play but must be slightly frustrating for beginners as you're never really sure how things will preform from one game to the next. Marines might seem boring but sometimes, when you're learning the game, boring is good.
None of this is to say that the Orks are a bad army. On the contrary, in the hands of a good player they can be as deadly as any other in the game. However, I think that it would take a while to get that proficient with Orks and I think trying to learn the game AND a complex army at the same time could be tricky. Plus, y'know, Space Marines are 8 foot tall, genetically engineer supermen who fire bullets that explode inside you! And who wouldn't love to start with that?