The cheapest and probably easiest is Lille. If you need to get to Paris its still easy on the train and no problem leaving the aircraft at Lille. Lille is very cheap and very friendly. Its also not far for a diversion and I guess you will know whether you are likely to make a visual arrival in good time before.
You will he held down below the CdG TMA well before Lognes so you will need to work out a let down anyway if above an undercast. Problems will arise if the undercast goes down to not much above 1,000 feet by which time unless it is local I suspect Lille will seem an attractive option. If its a bit above then with a descent to the east VMC below will work fine.
Reminds me of happy days stuck on the ground at Lognes with less than 400 feet for a solid twenty four hours. I well recall our thinking about an IFR departure but my friend ended up going commercial from CdG. He reckoned it was one of the worst flights he had ever had the turbulence was really unpleasant. They were indeed happy days to have stayed on the ground. The next day we did the channel in formation with a Yak, arriving into almost as miserable weather in the UK, but without the turbulence thank goodness. Nearly required a diversion mind you. I still remember going up the Eiffel tower while we were waiting for the weather, got less than half way up and we couldn't see a thing.