Originally Posted by
tods27
We did LGA-JFK transfer this spring on a Friday. Landed in LGA at 3:20 PM, collected bags and grabbed a taxi right by the baggage claim. The taxi ended up being about $70 (cheaper than Uber/Lyft and we didn't have to hike to the official pickup point) and took a good hour to get to JFK (clearly, 4:00 on a Friday is a bad time for this). Our flight out of JFK was at 7:25 PM and we had time to hang out in the LH lounge. Personally, I wouldn't dream of anything less than 3 hours for this transfer. 4 hours was comfortable.
Of course, getting to LGA will almost certainly require a connection on UA, so the EWR option is probably better.
I posted this long ago but my wife and I made it from door opening time at JFK T4 to the UA baggage desk at LGA in under 55 minutes. This is with immigration (with GE), waiting a short time for checked baggage, and taxi. I'm not suggesting this is routine but to note that it's not as far or bad as sometimes assumed when not at rush hour.