I don't think I would pick SEE over JML. However, I don't have his ultimate yet. I went Rey, SLKR, JML, SEE. If I were to do it over, I probably would have gone SLKR first, then Rey (just because the other two wouldn't have been out yet), JML, SEE. If I were starting today, possibly JMK or LV first, depending on how LV does.
Can't go wrong with SLKR as a first GL. He is very useful in both Conquest and Sith Raid. Rey is a lot better if paired with CAT.
Not sure where I am going next between Executor, JMK, and LV. I am finally taking the time to finish getting my 501st to g13 and my shore and range troopers to g13 as well. Then probably finish off getting the Executor toons to g13 and relic them while working on random JMK and LV toon gear.
If it is strictly a difference between SEE and JML I would go JML. Even though SEE might be easier, he really isn't all that useful and is easily beat by SLKR teams.