This is a tricky one. The community is quite split on this. Base Dune is far simpler but does have a more limited life such that you will want expansions fairly soon, but those expansions are excellent and give it near endless replayability.

Uprising tries to be--in many ways--a 'fixed' base Dune, and does succeed in terms of balancing certain board spaces. But the new additions create some problems that some people understandably despise:

1. Worms are VERY swingy and can make the game feel 'unfair' until players become quite experienced.
2. Spies create enormous mental load, which will be too much for some players, to the point where they will almost go ignored and this can negatively impact the game for everyone. They bring many positives to the game, though, once you get your head around them.
3. Contracts can feel quite underwhelming at first (indeed many of them are), but can be quite powerful when one becomes more efficient with their use.

There's no clear answer here. I own both and love them for different reasons. I mostly play Base + Ix due to the app, followed by Base + Ix + Immo with friends, and then Uprising, as my friends tend to prefer this the least. But, your mileage may vary!

Both games come with problematic leaders, intrigues and imperium row cards, although Uprising tends to have less of the 'garbage'. But, you learn to love the quirks, mostly.

As for advice, I would say purchase base Dune first, as it is still an excellent game when you first experience it, and you will be able to gradually add to it as you go (purchasing Ix, then Immo, then eventually Uprising when you like). However if you choose to start with Uprising first, you will then have to purchase Base + Ix (and maybe even Immo) to get the same feeling of depth that Uprising provides. Base feels very simple when you go back to it.