Why not both? You’ll need to run a server either way.
HA can export data to Prometheus. Setting up and running HA is much easier than figuring out how to get a set of different smart devices to export metrics to Prometheus/Influx. Let HA deal with that.
I live off grid, so energy monitoring is a big deal for me. HA is fine for “at a glance”, but if I want any kind of detail, I use grafana. I actually have my old openhab instance still running purely as I can’t be faffed setting up all the piping from MQTT into influx again.
It’s also possible to integrate the usage over time using a dynamic time window to get Wh figures from wattage, which is enormously useful for me, and is more accurate than the figures HA gives in their power system.
HA is dead useful for getting alerts when the laundry finishes, though - dumb machine, smart plug, look for a sudden drop in power. Also does all our climate control.
Seconded - HA's graphs are great for a simple "is this going up or down" glance but when you want to put a whole bunch of things together for comparison or perform aggregations or calculations, that's when you want Grafana et al.
HA is great, but it's not the answer to everything