Unless you have very specific needs or a complex setup, which is not the case of most users, I recommend to use extend the EFI partition created by windows from 100Mb to 512Mb (thus using a single EFI partition).
The reason is that the current Solus installed always select the first EFI partition it finds which result of some users wondering why they can't tell the installer to use the partition they have created for this specific purpose although it is correctly formatted, gets the flags, etc. or to some users not getting the bootloader installed at all because there wasn't enough free space on the default 100Mb partition created by windows.
Regarding the preferred installation option, it mainly depends on your tastes: If you want to define the size of the partitions yourself or if you don't want to have a swap partition, etc. You'll have to use the "custom one". The automatic one is good enough for most users.