AlwaysOn AG versus FCI

Throughout MS documentation for AlwaysOn Availability Groups (AG) and AlwaysOn Failover Cluster Instances (FCI) I see the following pattern:

• FCI is for HA scenarios.

• An AG synchronous secondary replica, co-located with the primary, is for HA scenarios.

• An AG asynchronous secondary replica, in a different datacenter, is for DR scenarios.

Here is an example MS link discussing this.

Since option #1 and #2 are both for HA scenarios, how do I decide between them?
If MS published costs and RPO/RTO metrics for both #1 and #2, it would be fairly easy to decide which I want.

Or perhaps there is a different way to understand the ROI differences between these options. For example, perhaps option #2 is best suited for VLDB's and option #1 is best suited for very high transaction volumes. I don't know.

So again, what is the selection criteria a DBA uses to choose between options #1 and #2?

To further complicate things, I know that options #1 and #2 can be combined! When is it wise to combine the two options? When is it pointless to combine the two options? I know when these options are combined, the AG no longer supports automatic fail-over. It's interesting trivia, but doesn't answer my question.

Incidentally, I intend on provisioning my final solution into Azure IaaS. If I use an Always On FCI, I will likely create the quasi-SAN using Storage Spaces Direct (S2D).
Update

I've found two articles that give a comparison. The first is MS docs, and the other is Choosing the Right Availability Tech. Both have a chart like this:

```
╔═════════════════════════════╦══════════════════════════╗
║ FCI ║ AG ║
╠═════════════════════════════╬══════════════════════════╣
║ Server Level ║ Database Level ║
╠═════════════════════════════╬══════════════════════════╣
║ Requires shared storage ║ Uses direct ║
║ (SAN or Storage Spaces ║ attached storage ║
║ Direct)

In general, FCI is more beneficial compared to AG because of various reasons already mentioned above. Of course, 2-node FCI is completely great but should not be built on top of storage spaces direct since S2D is known to be problematic in less than 4 nodes deployments (source).

For Azure, I would rather stick to a VSAN that is designed to work in 2 or 3 nodes scenarios like (example).

Here is a bit more information on FCI vs AG that you might find useful too

StackExchange Database Administrators Q#196793, answer score: 6