It activates when you take the Attack action, so Action Surge activates it a second time, and Haste lets you take the Attack action (for one attack), so that's a third time.
Eldritch Knights only good a bit later on and if you pick very specific souls.
Rune and Echo Knights are good out the gate.
Runes probably the best overall due to versatility eg archer option.
Eldritch Knights are pretty good out of the gate too and because of spells there is a ton of versatility there. Too much to really go through as there are a variety of high intelligence and low intelligence, high strength and low strength, combat and non-combat focused EK builds. Among combat-focused builds there are a variety of options too, including high DPR builds, a blaster that can keep up with a Warlock using Eldritch Blast and a Tank with Bladeward and Warcaster.
From a combat POV the big thing they get early is access to Protection from Evil and Good, Absorb Elements and Shield. These are 3 awesome spells, especially on a class with typically a high AC and a weak Dex and Wisdom saves. PEG is the cat's meow for a fighter with action surge going against an enemy that is going to charm or frighten you (most of which fall into one of the PEG catagories)
If you are a strength build and dumped dex but have a good intelligence they can get a ranged cantrip which will generally be better than throwing weapons. At 3rd and 4th level Booming Blade is pretty darn useful too. It and GFB become great again at 7th level with Warmagic at which point you will be outdamaging most other fighter builds.
The spell slots work really good if you pick up Hex through Fey Touched, or depending on the table through magic initiate Warlock .... although this does clash with War Magic a bit.
The 5e subclasses for 5e fans are in splat and setting books and have the sunk cost of their fandom's purchases of them holding the base class back.
I don't really get the tempest cleric love. It's always been a bit lackluster to me along with War.I don't know if that is really true. There are some great subclasses in the PHB IMO. Tempest Cleric is pretty awesome, so is Eldrictch Knight, Arcane Trickster, Shadow Monk, Divination and Enchantment Wizards and Vengence Paladins. I am sure there are good Druids, Bads and Barbarians too, but I don't play those often. Those examples might not be the best subclasses but they are all pretty good overall.
I like the variety offered in the other books though too, and there are some much more powerful subclass options there.
I was talking specifically about the fighter,I don't know if that is really true. There are some great subclasses in the PHB IMO. Tempest Cleric is pretty awesome, so is Eldrictch Knight, Arcane Trickster, Shadow Monk, Divination and Enchantment Wizards and Vengence Paladins. I am sure there are good Druids, Bads and Barbarians too, but I don't play those often. Those examples might not be the best subclasses but they are all pretty good overall.
I like the variety offered in the other books though too, and there are some much more powerful subclass options there.
I'm aware but the Rune Knight is a lot better at say level 3 for example.
I was talking specifically about the fighter,
The PHB fighter was designed to appease grognards who wanted fighters to be pure combat. Even the EK had many of its spells locked to evocation and abjuration when self buffing via transmutation and transport via conjuration would be better for combat AND have OOC use.
The mold wasn't broken and developed for actual 5e fans until splats and setting books were made. And even then,nnmagical fighters were barely touched, leaving many archetypes no supported in the manner desired.