Another thing with buying a season ticket from Hertford is that they allow you to use both stations in Hertford, therefore if there are problems on the Hertford North line then you can just as easily use the Hertford East line (just the other side of the town centre), which serves Liverpool Street via either Tottenham Hale or Seven Sisters. Journey times are slightly slower and tend to run every 30 minutes rather than the every 20 minutes from Hertford North

I think you have to deliberately purchase a ticket that says Hertford Stations to enable changing lines at will. Having said that, if there is a problem on Hertford North and you have a specific ticket you can easily swap to other line. It is just if you want to swap about yourself at whim.

I work nearer Liverpool St but live nearer Hertford North so I do swap about a bit.

The Hertford North trains are more frequent but slower, I think they are every 15 minutes or so from Hertford North. Never had a problem getting a seat unless there has been issues and I can count those times on one hand over the 5 years I have lived in Hertford.

Another thing with buying a season ticket from Hertford is that they allow you to use both stations in Hertford, therefore if there are problems on the Hertford North line then you can just as easily use the Hertford East line (just the other side of the town centre), which serves Liverpool Street via either Tottenham Hale or Seven Sisters. Journey times are slightly slower and tend to run every 30 minutes rather than the every 20 minutes from Hertford North