All recommended generals

Alfred, Roland, Cnut, El Cid, Basil II, Alexander Nevesky, and Timur are the must buy generals. After buying them other good generals include Harald, Subutai, Li Jing, Edward I, Barberossa, Alexios, and Baldwin.

Just use Elanor of Aquatine, she also has lobbyist 2. I don't see a point in Justinian unless you have his unique weapon. I only bought her for speed runs, nothing else. With good gens conquest is still possible without consul. In fact, it is more rewarding and fun. 

Matilda of Boulogne, Eleanor of Aquitaine and Athelstan are good supports you should get at some point. Though if you have the iap Olga, Athelstan isn't needed. Adil is also good and cheap second healer.

Cnut, Halfdan and Ivar are beasts at sea together and definitely worth getting, but if not all deployed, Cnut and Giovanni are best naval gens.

The "basic-use" gens propably are already mentioned.

Edit: if you don't have Richard and ever need interception skill, get Sunicas just in case. And Robert the Bruce in best or second best infantry general now. Even with iaps included, at least in top3.

I think many were already listed, and there are more lists somewhere here. Also from Discord you'll find up-to-date guide and lot of other info.

And, it heavily depends whether or not you have iaps, more precisely PoH.

Since the game is still "in progress" we don't have many pinned threads. So, the only available option right now is to "search" for it. Unfortunately, some discussions are obsolete/outdated and may be even misleading. I am afraid you have to use a "common sense" most of the time.

For example,

Alexander Nevsky.
1. He has a special weapon. Not a spectacular one, but it increases his cavalry capability by 40 points, improves 3 of his skills and increases his overall damage by 20 percent if his special unit (Boyars) is in his legion.
2. He has a special chapter. It is an interesting content (available only after purchasing this general) with nice rewards.
3. His cavalry points are relatively high.
4. His active skill enables him to atrack using a triple charge (and triple charge is one of the most devastating attacks in the game) with almost 100% probability once in 3 turns. So, it is similar to "Outburst". And "Outburst" is one of the best skills in the game.
5. He has 2 important skills for a carge cavalry general, namely "Polearm mastery" and "Cavalry tactician"
6. He doesn't have one excellent skill for charging cavalry, namely "Charge cavalry expert". But this skill is easily unlocked by gems.

All this put together makes Nevsky an excellent cavalry general. And so on...

Most of the time if a general has:

A. Personal weapon.
B. Special chapter.
C. Useful skills for units of his type.

- he is a good general, worthy of investments.

Here we have a dilemma: a "personal weapon" vs. a "special chapter" . I will buy Yelu because of his chapter, but his p2w weapon significantly weakens him in comparison to Gao (who has one of the best weapons in the game). Gao is an excellent general, in my opinion. But his special unit is very difficult to upgrade.

And Subutai is definitely worth buying because, unfortunately, we don't have many good f2p archers in the game. In comparison to other players I am less excited about his personal weapon. My Subutai feels good using Attila's weapon. If I get his personal weapon one day, that will be cool. If not, - it is not a tragedy either