Going back to the UK in September after several year absence, and I'm getting a little confused by my.....well, shall we say "wealth of choices" that suddenly have developed in rail travel - Virgin Rail ???

Long and short of it - needing to go from London to Rugby/Coventry area to see friends for a day, and possibly from London/Cardiff or another day trip. Don't really want to spend money a Rail pass if it's only going to be used 2 days. Looking for tips or suggestions to make my planning a little easier. Buy my tickets before we get there, or just wait until the day of our journey ? What in the heck is the difference between the good old British Rail and Virgin Rail ??? (other than Branson has more money of course....)

Any help is appreciated !