So, this is a very complex and interesting topic. I play a lot of green, and it's my absolute favorite color (yeah, I'm a big Timmy).
The short version of my answer is that it depends, but in general if I'm playing green I'm basically never playing mana rocks, unless there's a very specific reason to do so. My first choice is land-based ramp, with mana dorks coming second in general.
My "go to" and-based ramp spells, and those which I consider to be the best in a vacuum, are:
Three Visits,
Nature's Lore,
Farseek,
Into the North (which just requires you to play some snow lands),
Rampant Growth,
Sakura-Tribe Elder.
The reason to favor land-based ramp is pretty simple: artifacts can be removed (
Bane of Progress,
Vandalblast etc.) or shut down (
Collector Ouphe, etc.), whereas lands are mostly "safe" due to the fact that mass land destruction and other spells/permanents that mess with lands (
Blood Moon,
Back to Basics) are generally frowned upon in EDH.
That said, I don't just include all of the above mentioned spells in all of my green decks, and the reason is quite simple: I strongly believe that what makes an EDH deck strong is
synergy.
Therefore, if I'm playing a creature-based deck, that contains cards such as
Beast Whisperer and
Guardian Project, I will try to boost the number of creature-based ramp spells:
Sakura-Tribe Elder, but also
Wood Elves,
Yavimaya Dryad,
Springbloom Druid, and also mana dorks, such as
Birds of Paradise,
Llanowar Elves etc.
The reason is that in a creature-based decks, these ramps spells could still draw me a card or trigger some other synergies if they are drawn later in the game, so that they are never really dead.
An example of synergy-driven choice: in my
Hamza, Guardian of Arashin deck, I play
Devoted Druid, which I wouldn't normally play in a non-Elf deck. However, the synergy with +1/+1 counters is incredible.
If I'm playing an Enchantress deck, the same line of reasoning will lead me to include enchantment-based ramp spells:
Fertile Ground,
Overgrowth,
Utopia Sprawl...
If I'm playing a graveyard recursion deck, like
Meren of Clan Nel Toth, I want creatures that have a powerful effect when recurred from the graveyard: once more
Sakura-Tribe Elder, which is the all-star, but also
Dawntreader Elk and
Yavimaya Granger. In this particular deck, I believe that these cards are better than
Three Visits,
Cultivate and
Arcane Signet because of the much higher synergy they provide. Here is my current Meren list for reference:
https://deckstats.net/decks/149180/1755348-meren-aristocrats-midrange.
I have found that I basically never play "generically good" ramp spells such as
Cultivate, since there is always a more synergistic option. I've also wrote down a list of possible replacements for
Cultivate based on which kind of deck you're playing some time ago:
https://deckstats.net/decks/149180/2019513-replacements-for-cultivate.
The last thing I would like to say is that casual EDH player are way too low on mana dorks such as
Birds of Paradise (whereas cEDH players know their power really well). It's true that they can be removed by board wipes, but there is basically nothing that compares to them when it comes to speed: as far as 1 mana ramp, it's basically dorks or
Sol Ring.
They basically always give you at least 1 or 2 mana, and often much more, and if you're playing them they probably will trigger some card draw or other forms of card advantage in your deck. It's very anecdotal, but I once won a game through two
Cyclonic Rift with my Xenagos deck because I had
Guardian Project and three mana elves, so that after every
Rift I could just dump those into play and draw 3 cards.
I could probably go on even more with considerations on ramp spells, but that's probably enough for the moment!