Alrighty, cool answer. So if I were to collect a Space Marines army, just as a... thought experiment... Which chapter should I choose? I know Dark Angels are the strongest in the current meta, but that probably makes them a nerf magnet in the next update, right? Any good reasons to collect one chapter over the others?
Unless you're planning on playing competitively, chasing the meta isn't necessary with marines, they're pretty interchangeable when it comes to more casual environments.
For starting out, I would suggest playing ultras or fists, as they're fairly solid all rounders, and once you get a few games under you belt you can decide if you want to branch out into another chapter (either don't paint you guys at first, or do paint them but use a custom color scheme. If you do change chapters, you don't want a bunch of guys in Ultramarine colors in a Blood Angels army).
As for collecting a specific chapter, outside of rules the big draw to chapters like DA is their unique units. Most chapters share the same list of units, but some have thier own special units, and some of them also don't have something from the core list.
For example, the dark angels have two unique aircraft (both of which rock), three unique landspeeder variants, a number of unique biker models, a unique terminator squad (deathwing knights. They're badass), a few more weapon opitions for thier stock terminators, unique terminator characters, and unique support models like a terminator apothecary (who is amazing because unlike the normal apothecary, he has a gun), and in exchange for getting all that stuff, they only lose a handful of units, I think it's just sternguard vets and vanguard vets (shooty and stabby/hammery elite sqauds).
The blood angels have a bunch of unique assault infantry, unique dreadnoughts, and a unique tank that was pretty cool before the reaper grav tank made it obsolete, but I don't know what they lose.
Space wolves also get unique stuff, like a unique flyer, some unique weapons, and a bunch of wolves and mutant wolfman they can deploy. Also not sure what they give up, aside from thier dignity*.
None of the chapters that get special stuff lose out on basics, so if you start with an HQ and a few troops you should be fine to branch out from there. Here's a quick, probably mostly accurate rundown:
Ultras: all rounders
Fists: also all rounders, with added bonuses against dug in opponents.
White Scars: Bike Assault
Black Templars: Assault but specifically with infantry
Salamanders: resisting high volume of fire attacks
Blood angels: jump pack assault, also melee in general
Raven Guard: all rounders
Iron hands: tanks, heavy weapons. Don't play iron hands if you're thin skinned, some people are still salty about them being super broken at the end of 8th edition.
Space wolves: assault again.
Dark Angels: All rounders, but can really focus in on excelling with either infantry, bikes, or terminators and bladeguard.
*Why yes, I
do play dark angels, how did you know?