Ubuntu installation partitioning: Logical or primary?

The short answer "it does not matter much".

MBR partitioning scheme allows you to have up to 4 partitions on a drive, one of those partitions can be an "extended partition", which acts as a container for any number of "logical partitions". The partitions which are not inside the extended partition are called "primary partitions".

There's no difference in how they function or anything. So, if you don't have specific reasons, just go with the default choice.

I think the explanation below is too basic for the OP, but I think it could be useful for a beginner.

That choice between "primary" and "logical" has always seemed confusing to me, because the terms are not alternatives (logically, I mean).

For a clear definition of the terms - there is a good answer here.

The difference between "primary" and "logical" is imposed by the limits of the MBR partition scheme, where a drive can only contain 4 partitions. When such partitions are created on a such derive, they are called "primary". In order to go above that limit, there is the "extended" partition, which is different from the primary in that it is not a partition on which you can put things and boot from it, but a sort of container for other partitions, a sort of virtual "drive" which can include more than 4 partitions.

In layman's words: when a partition is created simply on a drive (in a MBR partition-scheme), it is called "primary", when it is created within an extended partition, it is called "logical".

All that is rather clear.

What about the confusion? There is no confusion when partitioning with Gparted or similar tools which provide a choice between creating primary or extended partitions: we are not asked whether we want "logical" ones, because we need an extended one before having a logical one, and when we create a partition within an extended one, the new partition can only be logical.

The real choice is between primary or extended, and that's what we see in an partitioning tool.

The GUI tool in the question is an installer, not a partitioning tool, and the choice it provides can be misleading: if we select "primary", that will result in what the terms says; but if we select "logical", it will create an extended partition containing one logical partition.

That GUI doesn't say anything about "extended" partitions, we are supposed to know that a logical partition can only be withing an extended one, etc. But the fact that it doesn't ask if we want more than one logical partition within that extended one, and simply creates one logical that fills the entire extended partition is confusing to me. I don't understand what the use of that could be.