If you were to create an RPG game, what inventory style would you use?

The two that I'm stuck between are 1. Minecraft, where there's a fixed amount of spaces for items.
2. Skyrim, where you can pick up as much as you want, but every item has a weight and once you reach your weight limit you will receive certain punishments such as slowness or weakness.

I think No. 2 is definitely better. Due to the fact that you will get punished for having too many items, it makes gameplay much more dynamic and interesting when you have to think about the weight of said items. In Minecraft, you can easily just throw away any item you don't need and switch, or just store everything in a chest that can be created pretty much anywhere with some wood. While you can do both of those things in Skyrim, it is not as helpful or easy. It makes you think about each item you take, rather than about how can you make this work or where you can store the items you just took.

That really depends on the game's style.

Style 1 leads itself better to games with lower… Grittiness for want of a better term. If you players will regularly be hauling around massive construction pieces or items that are very large in the game world this style is abstract enough to help with suspension of disbelief.

If you don't plan on penalizing a player for going over-weight, just preventing them from picking-up anything else, this is also the better option.

It is also good in games where potential content of your inventory is large, but the in-game 'value' of each object is relatively low. (See style 2 for a better explanation).

It is also easier to code and add to, because you don't need to be concerned with a new item's weight.

Style 2 is seen more often in gritty games. Also fairly common, at least recently, is a penalty for going over instead of an outright prohibition against new objects. Example: You can pickup everything in Skyrim at once (in theory) but after a specific point you are greatly slowed, unable to sprint, and can't fast travel.

Style 2 also lends itself well in games where the content of your inventory has great 'value'. An example of this would be a survival game. Supplies are generally quite limited in Survival games, and each is very important to the character. Style 2 can force choices on the player such as; "do I take this five pounds of food, or this gun and hope I can use it to get food?"