BritRail pass, EuroRail pass, or National Rail?

I'm going to England for about half a month to a month in May - June.

I'm considering buying a train pass in advanced, but I'm confused as to what I should get, or what would be the cheapest solution?



I know I want to go to Salisbury for Stonehenge, Scotland, and possibly Ireland.. And of course I'd want the trips to be spread out.

I noticed that BritRails Flexipass says that I'm able to travel for x amount of days with x amount of months. How are those days counted? By time spent on train? Or is one trip counted as a day?



Any suggestions and tips would be amazing. I'll be with one other person.BritRail pass, EuroRail pass, or National Rail?
The Britrail Pass is not valid in the Republic of Ireland, but is still good value. The Flexipass is valid for as many train journeys you wish to make on the days you decide to travel. The Eurorail Pass is valid in most European countries except the U.K.. Buying individual tickets for each journey you make on the trains in the U.K. is a far more expensive option unless you buy the cheaper advance purchase tickets, tieing you to specifically timed journeys. The joy of a Britrail pass is that you can have flexible plans and hop on and off trains at a whim, which is easy as the network is dense and frequent. Between London (Kings Cross) and Edinburgh for example there are generally trains every 30 minutes,

and with the Britrail Pass you could break your journey at interesting towns on route such as York and Durham