Friends are going to Tokyo Monday for 2 weeks. They are thinking of going to Nikko as a day trip by train or bullet train. We took a one day bus tour (and we seldom take group bus tours)and liked it because we went to several other places (a lake, etc.) on the same trip and still had plenty of time at Nikko. For people who are not adventurous, what do you think...the train (how far a walk from the station to the temple?) or a bus group experience?

I seldom recommend bus tours, but this might be one case where I might. I think the bus tour would be nice if they are not as adventurous as you are. The train is easy enough, sure, but they might see more and get to meet a few people as well. They could certainly decide up to the day before going how they do it...that way they could see how they feel about doing it on their own vs. a tour.

FOr people who are not adventurous then the bus tour that picks them up from the hotel would be best, I think.

Taking the train would be a bit more involved. Getting to JR Tokyo station then transferring to the Nikko line. Or getting to the Tobu Asakusa station and then the Tobu train (not JR and not shinkansen) to Nikko.

You could take a look at this:
http://www.jnto.go.jp/eng/location/rtg/pdf/pg-302.pdf

Sounds like you can personally recommend the bus trip to them. Hard to beat that considering your assessment that they are not too adventurous. However, they must have some sense of adventure as they are going to Japan for two weeks.

oops, one route would be getting to JR Tokyo station, and then taking the shinkansen and then connecting to JR Nikko line. So, good chance that they would have to make two train transfers if going by JR instead of Tobu.

There is now once-daily through JR train, Limited Express Nikko, from Shinjuku to Tobu-Nikko station, and a connecting service (Limited Express Spacia) via Shimo-Imaichi 3 times daily. 3900 yen one-way, taking 2 hours. You need to buy a supplementary ticket to travel on one of these trains if you have a JR Pass - see www.japanrailpass.net
The temple and shrine complex is around 5 min away by frequent bus that leaves outside Nikko station, or 25 minutes walk. It should be easy to find your way around, as English signs are everywhere and ticket office sells good guides in English. To get to Kegon-waterfall and Chuzenji-lake, take a bus from the temple area to Chuzenji-onsen (40 min, 1100 yen one-way). There's English announcement on board. You can buy a 'free pass' that includes roundtrip train travel with compulsory seat reservation and free bus rides in the Nikko/Chuzenji area for 7800 yen.
As Nikko is a popular destination for foreign visitors (often they outnumber Japanese!), independent tour is very doable, even without much Japanese. But if you want a hassle-free trip with English-speaking guide, a bus tour from Tokyo may be a wise choice - JTB Sunrisetours do one from 11,500 yen http://www.jtbgmt.com/sunrisetour/te14/

Thanks, All! I sent on your responses to our friends. It will be interesting to hear about their Nikko day on their return.

Elainee, just so they know, the autumn leaves are at their peak in the first part of Nov. in Nikko. They are going to have a lot of company either way they decide to go there.