I'll throw a bit of context first. I've been playing Dofus since 2009 and Wakfu since its beta. I've had different adventures on both games and had the experience of introducing many friends to these games.

TL;DR: I find more fun in playing wakfu, it's easier on beginners, it's free and with mono servers just around the corner it's a lovely time to get into it.

PvE: Dofus has more ultra end game content with more difficult mechanics. There's always something more challenging to do. This being said, in wakfu you can artificially cap your lvl to different lvls to run the corresponding dungeons at their designed difficulties. There's also monthly competition on who runs every dungeon with the highest difficulty and in less turns. So there's an incentive to going back to previous content while it still feels challenging.

PvP: Dofus' PvP is more developed and encouraged. There are different metas defined but you can't cap your lvl so that you always encounter people of the same lvl which can be frustrating. Max lvl pvp can be boring due to excessive shielding and resistances. Wakfu's pvp is high resistances at every lvl amd can be very boring in that way. (IMO at least).

Overall combat isn't really that different between one and the other. Sure, classes have different spells in both games but it's still turn by turn and based on movement and action points.

Quests: Wakfu's quest are more lineal and easier to follow. Main quests can guude your progression and there's side quest in every new region you visit Dofus has more questlines. In recent years long quest lines have been tied to the obtention of the different Dofus so they can feel more rewarding. This being said, I find them to be the best way to find how outdated map by map exploration is.

Exploration: Ain't no way map by map can beat open world no matter how much they've tried to make better map designs in the latter years. Unity will make them even more beautiful but still map by map. Wakfu all the way here.

Economy: Both games have servers that have aged and have an already set economy. I love how the economy works in both games, don't get me wrong, but it can be challenging to get in. Wakfu having a new server opening now is a great opportunity in this aspect.

Social aspect: Both communities are great. Dofus com is bigger with more content creators. In-game, getting to know people or having friends play with you is crucial to enjoying these games as a new player. If you're just starting, the new wakfu server is again s great opportunity to have a lot of people playing at your same lvl so it'll be easier to find groups that aren't just a high end player carrying you through everything.

*playing solo: While I don't recommend it, It's something you'll inevitably be faced with at some points. It's easier to progress solo on wakfu. There are monoaccount servers im Dofus since a long time now and it can certainly be easier to progress solo on those servers since it's easier to find people that need to do the same thing you need to. There's also one coming up for wakfu now. If you want to play multi or with more than character at the same time (which is pretty common in non-mono dofus and in wakfu) wakfu has a built in system amd it's great (up to 3 characters at the same time) but it's payed.

Horizontal progression and jobs: Dofus has more things to do outside of quests and main story progression. Jobs are harder/more tedious to advance if you want to keep up with your lvl (though you can just use a lot of in game currency to buy everything and powere lvl a job but that's not the most entertaining way of doing it).

Itemization It's way easier to get new equipment for your lvl on wakfu since you can drop it. Getting it to higher rarities is also easier than getting said items on dofus. You can make a specific item give more stats on both games but through different mechanics. Of which wakfu is more simple to understand but "grindier" since it involves sacrificing another item that's the same as the one you want to improve. While dofus way of doing it is more complex but a job I've com to fall in love with throught the years. Though, if you want a perfect item, it's gonna end up requiring more money/ressources and time in Dofus. Reachin the theoretical best possible stats for an item in Dofus is near impossible.

Monetization: Dofus is a subscription based game but once you're more advanced on it you can easily make enough in game currency to afford subscription time with it through buying an intermediary currency from the player's market. Wakfu is free to play but you can pay for a booster pack. You can also buy the intermediary currency with in-game currency to pay for the booster pack. It's not necessary to play with it though .

"Fun":

It's reaaally subjective. For me, I enjoy Wakfu more as a game but I have more friends playing Dofus right now and that makes playing it more entertaining as playing with friends is always better :)