NRT - HND transfer time

Hi
I am on a flight planned from abroad to Narita morning arrival, transfering to a domestic flight on the afternoon from Haneda. JAL to JAL. All on the same ticket. There is 6 hours between the flights.

Is that enough for transfer, considering delays of arrival, customs queues, taffic delays, etc?

I heard there is a direct bus as well as a somewhat direct local/express train there. Would bus or train be better?

Yes...I'll be doing a Chicago-Narita and Haneda-Nagasaki transfer with 4:30hrs between them on the same ticket and ANA even suggested an earlier flight by 1 hour on their scheduling. 6 hours is more than enough.

Which date, what time flights?
To ask about this is to verify that you need to avoid Morning rush or not.

The delay of itn'l flights is the biggest cause due to weather conditions,
but if it is regular flights you can confirm 7 days flight history at "Flightradar24" in advance.
https://www.flightradar24.com/
(sample, no need "log in", free)
https://www.flightradar24.com/data/flights/jl11

Transportation btw airports is detailed in both airport sites.
There is also a direct bus that goes through the bay area,
also direct trains(no seat reservation) are operating after morning rush hour.

The bus runs also during morning rush hour,
but there is a bit risk by traffic jam(not so serious) or accident.
Also by rail possible during rush hour,
but it is caught in congestion due to the transit in the downtown area in Tokyo.
You can search at Google MAP and HyperDia very easy.

The fastest train is around 85 min
via Nippori by LtdExp SkyLiner fr NRT and Shinagawa.
(Keisei - JR-East - Keikyu/railway companies)
http://www.keisei.co.jp/keisei/tetudou/skyliner/us/index.php
http://www.keisei.co.jp/keisei/tetudou/skyliner/us/ae_outline/index.ph...
This is direct train (Not LtdExp) is about 90 min.
http://www.keisei.co.jp/keisei/tetudou/skyliner/us/nrt_access/index.ph...

Direct bus is about 80 min if no traffic jam and accident.
You can check real time traffic conditions at Google MAP,
but can not predict the future a few minutes ahead.
https://goo.gl/maps/Lx8NweE2muN2
Bay area Expway(Wangan line) is wider than mid Tokyo, but larger trucks a lot.
http://neko-expwy.up.n.seesaa.net/neko-expwy/image/KASAIJCT01.JPG
So train is safer if it is a holiday(SAT, Sun, National holidays) or Rainy day.

I would recommend limousine bus in which your seat is secured. In general the bus runs faster than the timetable. You can see the current travel time from their website.

http://www.limousinebus.co.jp/cgi-bin/realtime/busdata_e.cgi

I feel the bus is a bit expensive compared to express train though.

You say the train can be congested but I suppose you do not mean congested as in delayed?

If I am already seated from Narita airport, maybe no problem if I put my luggage very close. Or maybe too much struggle?

On the bus, you don't have to worry about handling your luggage through the train or the stations to get to the airport. It rides under you on the limousine bus. That is the option I will take.

If I am already seated from Narita airport, maybe no problem if I put my luggage very close. Or maybe too much struggle?

At Narita airport you can probably take your seat, but note that it is a commuter type train. The seat is so-called bench seat and if you take wheel suitcase, you must hold it during the whole travel which will take about 2 hours. Well, it is like a "work" for two hours. The train is like subway (in fact it is subway in some section) and can be very crowded. Even if it is not the rush hour, it is going through the world's most crowded city.

Personally I have experienced both the Keisei-Subway-Keikyu route and the limousine bus, and for me bus is much better. I googled and found all people says that bus is much better, as JohnB wrote.

If I have a same day transfer, I now take the bus. I prefer the views and ease of travel after a long flight. The only place the bus seems to get slowed down is on the expressways close to Haneda. The rest of the route along the bay is clear driving.

If it's after dark, I sometimes take the Keisei/Keikyu train as half of the route is underground. Most of the time I've taken it I've had a short transfer in Aoto, but I just got off the train from Narita, stood on the same platform, and the next train that pulled up took me Haneda. I only use the N'Ex if I'm just going into Tokyo or Yokohama.

The Limosine bus may be more expensive, but it totally makes up for it due to convenience and comfort. On average, it took me between 50-90 minutes on the Limosine bus. Never underestimate how annoying moving luggage is on trains through large stations, specifically if there are transfers (I can't remember if there is)....