First of all welcome to
40k! Its always awesome to meet and see new people getting into the game
But,
TO THE ARMY.
Now, honestly I think the first one is the best, its simple, its fluffy, and its symmetrical (my OCD thanks you), and it should be a fun but effective list at small games as long as you play smart with your jump troops!
#2: This is a close runner up for the list, honestly there is nothing WRONG with this list, I am just a fan of the extra mobility you get with he jump packs, however list two would be a TAD better in small objective games.
#3: I'm gonna be honest with you, Honor Guard are not really worth it unless your have an expensive
HQ to protect, and even then they are still more of a flavor choice, yeah they can get alot of special weapons and don't get me wrong, they have their uses, just not here, too much of a point sink for such a small unit, and also it takes points away from your troops, which in lower point levels, are your most important option. Plus you only have one real troop choice, on assault and one death company, which are amazing! Buuuuttttt...
#4 First up, your Death Company can't take or hold or even contest objectives, so, sad face. In an objective game you would either have to kill everything or lose. Also, I can see what your thinking was with the Termi Priests, but remember, a model with Termi armor can not preform sweeping advance, and if only one model in the unit has terminator armor than the rest of the unit can't perfom sweeping advance (that rule I'm a bit fuzzy on, haven't check it in a while but I am 90% sure I'm right) so most of what your assault and kill with the angry marines with just run away the first chance they get. One more thing, Death company are tough, SURPRISINGLY tough, but marines are still marines and they don't do well on open ground in such small numbers, Death Company need some metal boxes to hide in or jump packs to reach their full potential in a game.
Now that we have that out of the way, here are some tips.
In all your lists you seem to love Infernus pistols, and as soft and fluffy as they are, they are not that effective, you need to get REALLY close to get the melta rule working for you, so honestly you dont really need them, save the points for Meltas or Flamers for your troops.
Librarians... Not really as assaulty as you may think, with some of the new rules for psychic powers remember there is always a chance your power can be nullified, adn with people like the Nids or the Space Elves running around those chances only go up. Librarians are generally delegated to a more support role in the army rather than a heavy hitter, which he can still do don't get me wrong! Anyways like in your first list, take Shield of Sanguinius, that way your boys can get up the board in one piece and you don't need to take those silly combat shields
which will save you some points for special weapons. The other powers in such a list could vary, but just keep in mind what you want your model to be doing on the battlefield. (Might of Heroes could give your some good lulz with your Assault Marines.)
You really don't need to have your Vet Sergeants so tooled up, you cut out their equipment (leaving the power weapon of your choice) and replace your Liby with a Reclusiarch with a jump pack, and have enough points left over for some Meltas for your jump squads. That you allow your squads to hit MUCH harder and the
HQ can lay down some hurt for himself.
ANYWHO these are all just suggestions and at the end of the day your the one that puts them on the table, just keep spitballing lists until your find one that feels right, Im mean thats what this fourm is here for after all
FOR THE EMPORA!!
But yeah at 500 points there is not much your Assault Squads can't take in a fight, you would just have to watch out for some horde units like 20 or 30 man Ork blobs and such, in which case that flamer fuel would be worth its weight in gold.