I will weigh in just because I have always lusted after an e-type.
A few have said if you want a car to drive get the e-type. Certainly a more modern car, better able to keep up with traffic, keep you dry when it is wet out or warm when it is cold out. While true and while definitely the e-type is a winner if you are talking about highway driving, that being said, while I have never driven a J2, a friend took me for a ride in a TB a couple ears ago. What a hoot, blast to zip around town in, a fairly unique driving experience, even more so than an E or other 60s british sports cars. feels like you are going fast even when you are going slow.
Both are beautiful cars, as stated by many the J2 is much rarer than the E and less likely to come along.
It sounds like you have a likelihood of purchases of this nature in the future. So, if that is the case, maybe J2 now and E later.
For me a chance to own either would probably be a once in a lifetime never another chance for anything like again in my life, so a harder decision, but if an e-type could still be viable purchase in the foreseeable future the J2 seems like the pick. But it is you choice and your bucks.