I'd recommend the original series, even though it isn't as good as Ultraseven (IMO). As for what's fan-subbed, I think Nexus is pretty good, but it has a completely different tone from the other Ultraman shows, so it might not be a good place to start.
I like Ultraman Leo and Ultraman Gaia, but I don't think those have been subbed.
I like Ultraman Leo and Ultraman Gaia, but I don't think those have been subbed.