Bundle SKU which includes both HW+SW. Example: SRX4100-SYS-JB-AC
If you purchase the seperate HW+SW you will need a support SKU for the software and a seperate SKU for the HW.
If you buy bundle SKU there is only on support SKU for SW+HW (depending on support level).
In general I would recommend just looking at the bundle SKUs.
JSE (Enhanced) adds support for firewalling based on App identification - eg. block facebook, but allow youtube.
You can also do routing and QoS decissions based on application identification.
If you intend to buy subscription for IPS, UTM or similar, JSE functionality will be included in these... but only for so long as your subscription lasts.... so if these features are needed as well, just go for JSB.