Ok, now I understand the question about round bases - Bakhara, you meant the infantry and not the vehicles, correct?
Vehicles aren't required to be based at all, as you probably already know. Some of the other guys here have already answered pretty sufficiently, but I'll just confirm. Yes, these days round bases are somewhat easier to come by. The long rectangular ones are second easiest to find, and the square ones hardest to find of all.
I currently have two painted armies and I am working on a third. For the two complete armies I have, (Loyalist Marines and Chaos Marines), the Loyalists are on the long rectangle bases and the Chaos Marines are on round bases. This choice was deliberate for me, and I'll explain why as succinctly as I can. It's hard to fully appreciate until you have played a few games with either style base, but in game terms, it's far better to have your troops on the rectangular bases. There are a lot more "shenanigans" you can pull with the long bases (and I used the term "shenanigans" loosely here, as the rules in E:A are so tight that almost nothing feels "gamey").
The Space Marines, who really are a "finesse" army in E:A and require very precise tactics to win with consistently, almost need to be on the rectangular bases. And, for me, this fits in with their role as an asymmetric warfare elite force that relies on cunning and "dirty tricks" to achieve objectives.
Chaos Space Marine forces, on the other hand, tend to be looser collections of cut-throats, malcontents, and every-man-for-himself types that don't operate with the scalpel-like precision of the loyalists. So, in addition to their lack of the "And They Shall Know No Fear" special rule, I wanted to represent this relative lack of cohesion by having them on the less-efficient round bases. So my decision to put my
CSM on round bases was kind of a self-imposed nerf. It was also an aesthetic choice. The round bases take up more table space, making the force appear much more horde-like and disorganized.
The third army I'm working on? Cadians. The bases? You guessed it. Square!
This is primarily an aesthetic decision for me, but it's also because I think the square bases probably function in-game somewhere between round and rectangular.
TL;DR Rectangular bases are by far the most efficient from a gameplay standpoint, but people base their models differently for reasons such as availability, aesthetic, or theme.
Rectangular bases should be available from Steel Crown for those interested.
Bakhara, I've seen some of your other posts and it looks like you are into tournament play. Totally not trying to proselytize here, but if you are interested in a tight ruleset for competitive play, Epic Armageddon is universally regarded as the tighter and more balanced ruleset. I personally feel it's the tightest rule set that
GW ever came up with. However, I can definitely see the viewpoint that it is not as "robust" or "fun" as the 2nd edition rules. It can feel a bit Spartan at times. I also see that you're in Pasadena, which isn't so far. We have about 15 or so people here in LA who play Epic, but all of us play under the Armageddon rules.
