I did the same thing as
@scubadada, except in the summer of 2016 on the RS1.
Since I was already in Europe for work and since my son needed to visit grandma, we flew in (to Hurghada) with CONDOR from Munich. I booked the Marriot there (before and after, I think 1 night each) not through Agressor since I found their price to be north of twice of at the going rate then. But I did, despite reading of much lower cost options book the transfer through Agressor, since I wanted to make sure the boat waits for us ... in case...
We loved both weeks (northern first, southern second in our case). We also just had 40 or so dives under our belt then, Bonaire having been the only place we've been diving prior other than the initial OW class. But we had our Nitrox and AOW certs. I do agree, the northern dives are on average a bit deeper and with more current. Dinghy drops were at times in fairly wavey areas and, due to the current, some entries were negative. All new to us, but we all liked it just fine. Of course it was quite warm then... My (skinny) son was fine in his 3mm suit, no hood and I was fine in my 3mm shorty no hood.
I found St. John on the Southern route to be a little special place... Almost like English walled gardens, except all walls are coral. On our trip, we happened to not find the dolphins to snorkel with, but it was an amazing trip nevertheless.
@scubadada 's trip report is excellent.
Those deeper dives BTW are mostly on walls, as the "airhog" I usually staied a little higher than most for part of the dive.
We at times encountered some faster currents, but no "funky" currents (down or up or out...). For both itineraries I do recommend that each diver bring an SMB and can deploy it. Just seems to make sense, ... Agressor does not insist on it so (or did not then). I also always had a light, a mirror and a Nautilus on me.... just did not want to miss the boat...
I think you will like either itinerary if you need to pick one that fits in a time plan. If you can choose, then maybe southern.... if you really can choose, then definitely both
One word of warning: I speak with much less experience to back it up than most here. This was so far our only LOB trip ((a time and budget thing, if I could I would do it all again tomorrow otherwise... well, going elsewhere to see what is going on there makes sense too of course and this winter we will get to experience a small corner of the Phillipines, ... details still TBD)
Edit: Unless I count "retirement" (at some point) as a trip, it is extremely likely that this will have been the only dive trip ever during which we manage to double our dive counts...