My vote is KHPN. Last time we were there Millionaire got our business. Very helpful, very nice. I'm pretty sure you could make it a (long) day trip by going in and out there. Land, be at the train station 30 mins later, 45 mins to Grand Central, mess around 5-6 hours, come back and leave.
I looked at the NJ airport (Linden) but found volumes of bad reviews and questionable business practices to the point of marking it off even though it looked easy / very close to NJ Transit / easy-in to Penn Station.
A few mentioned walking to the train station at KHPN. I think they are confusing KHPN with another airport. There's no train station within less than an 60-90 minute walk that I'm aware of.
The only "eastern corridor" unique stuff I had last time going up there (from Arkansas):
1) They added over 110nm of routing to what was supposed to be a 170nm final leg into the city. Luckily I decided to stop for full fuel thinking there'd might be some "fun" routings I've heard so much about. When I got my first "advise when ready to copy" with an amended clearance, I wanted to respond with "you're kidding, right?" when controller got finished dictating. In retrospect it was no big deal with 9-10 elements to the clearance. Yet, prior to that point, I was used to 2, maybe 3 points added to a clearance and the verbose instructions made me utter to my wife, "we're not in Kansas anymore". To add to the fun, I got 2 additional amended clearances before landing, but they were minor revisions in comparison. Very glad I brushed up on entering, editing and fully using flight plans in the 430/530 before going / would have been very hard otherwise with all that was going on -- at the time in our previous plane that didn't have an autopilot -- and in IMC for the last 90 mins into the City.
2) On the way out I looked at the SkewTs. The bases were around 1500 with tops around 7000. I file for 8000. They give me 6000. No problem -- we depart. 30 minutes later I ask for higher and am told one word: "unable". 60 mins later still in IMC without an autopilot I again ask for higher. "Unable". By Western PA, they finally let me climb to 8000 and be in the clear. It made me realize you absolutely don't want to fly anything less than a FIKI aircraft up there in Winter if there's any chance of freezing -- no matter how thin the layers are. Around here 1000-2000 foot layers are no big deal in the Winter as you can slip right through them with typically no accumulation / ATC is very accommodating. Up there, a "minor layer" could likely turn into the need to declare an emergency due to the airspace being so congested and no other place to put you...
Other than that, I found ATC nice, helpful, accommodating -- but rapid. All in all, I look very forward to going again (with an autopilot this time) and will definitely go back to KHPN.