Grafana is obviously the main one, their original product and the most popular one. It's to aggregate data from various sources and make dashboards.
Loki is a logs collector that I personally didn't try but I think it's popular. They released it after Grafana.
I don't know the third one.
The last one seems to be a wrapper around Prometheus (a metrics collector/database).
Fair to assume you should start with Grafana. For the source, if you don't have a Prometheus instance, you can test it with any SQL database.
Grafana is obviously the main one, their original product and the most popular one. It's to aggregate data from various sources and make dashboards.
Loki is a logs collector that I personally didn't try but I think it's popular. They released it after Grafana.
I don't know the third one.
The last one seems to be a wrapper around Prometheus (a metrics collector/database).
Fair to assume you should start with Grafana. For the source, if you don't have a Prometheus instance, you can test it with any SQL database.