I am in the process of reinstalling Ubuntu.
I was prompted to choose a logical or a primary partition. I've never seen this dialog box before -- before it just told me to choose the mount point and the format.
Should I choose logical or primary? The default is logical
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.
For root and swap you can choose logical or primary your choice but remember you can only have 4 primary partitions on the hard disk after that no more partitions(logical or primary) will be created(i mean you cannot create partitions after that). If you want to create partitions you should convert one primary to extended(or logical) partition and split that into several partitions.
so if you are out of primary partitions then its recommended to install both in logical, if not you can install them on primary partitions(if you don't have any use of primary partitions in future like installing windows again)
I hope that helps