We did Vimy Ridge in 2010 and saw some of the DDay beaches in 2012. We didn't have a lot of time to do either, but both were very poignant.
We did Vimy Ridge as a day trip from Paris. Took the train to Arras, got a taxi out to the site, spent some time walking around and got a taxi back to Arras, had a bite to eat and back to Paris then moved on to Strasbourg (which was why we were a little rushed as we were heading for a different city). We visited the monument and went to the museum area. Visited a few of the cemeteries. The monument is beautiful - I guess some years ago they did a restoration of it and it's gorgeous.
When we visited the DDay beaches, we had a car rental and the first night we visited the Juno Beach Center - I'm not a big war buff, but if was especially poignant - watching the videos almost made me cry. We were staying with a lovely couple (via couchsurfing) in a tiny place called Amblie, and the next day he took us around to some of the beaches and towns, taking us to the Benys-sur-Mer cemetery, the DDay landing site, showed us Canada House (I think it's called)...pointed out the information around the town showing scenes of the war.
So you have WW1 and WW2. I guess it may be easier as a day trip from Paris to do Vimy Ridge on your own via public transport, but I also think you can do tours of the beaches with tour companies. I still remember the cab driver they called for us at Vimy Ridge - he didn't speak much English, but he gave us an armload of pamphlets from his trunk and drove us past a few of the German cemeteries on the way back to Arras - nice fellow - he even charged less than the taxi from Arras to Vimy (I don't think he was an 'official' taxi driver - I'm pretty sure there was no meter in the taxi).
Just consulted with hubby and for him, Vimy Ridge won hands down. For him, the beaches were just 'beaches' but he felt Vimy Ridge meant a little more as Canadians. (His words).