What's the most rewarding difficulty curve?

Most rewarding difficulty curve:

I think the two main ones are 1. the game starts off easy, and progressively gets more difficult, and 2. the opposite, where the game starts off extremely challenging but becomes easier as you gain more levels and equipment. Of course, there are exceptions - the Souls games start off challenging and never let up, and some games will start off easy and then suddenly hit you with a wake up call mission that signals a massive spile in difficulty.

I've found that I enjoy games that start off difficult, but allow you to progressively make it easier the most; these games tend to still have very challenging boss fights, but there's a real sense of achievement when you realize you no longer have trouble taking out those really tough mooks, and feel far more powerful when nearing endgame.

A decent example of this would be Fire Emblem: Radiant Dawn - the game starts off very, very rough, with pretty much all of your units capable of being almost oneshot by most normal enemy units, and continually gets more and more difficult until you reach midgame and get Ike and can proceed to steamroll the rest of the game. The bossfights and endgame levels are designed to still be challenging, but you're given a much larger variety of ways to approach them, and all of the units associated with Ike are quite powerful in their own ways; in comparison, nearly every pre-Ike unit, save for Micaiah and Edward and a few others, is rather mediocre. So, as a result, getting Ike feels great and almost like a reward in and of itself.

This really isn't specific to just one sort of game, though. What are your thoughts?

Thanks keep sharing..