Fast Leveling

I'm just trying to level up. The game doesn't seem to offer many options, I find the extra island missions to give the most EXP. Any suggestions I'm PLVL 44 right now.

Extra island should let you level 2~ levels a day till levl 60, when it should be 1 a day.

The only way to move faster is to use gems.

Not sure how strong your team is, best experience per stamina is final level of arlong park loguetown and twin capes when they are half stamina. They each give higher experience/stamina than 30 stamina fortnight isle. (For reference it is something like 730/6 for arlong park final, 820/6 for loguetown final, and I honestly cannot remember laboon but it should be highest of them).

If none of those islands are up or you can't handle them then the 15 stamina event or 20 stamina gold cave is best option. Something of note is the intermediate gold cave can provide the highest experience/stamina at 3200/20 but that is rng based as you have to encounter fullbody during the run for that to happen. Otherwise the 15 stamina is best bet for more consistent experience, plus you can actually gain character experience from that one.

Another possibility is to farm the 10th level on loguetown when it is half stamina (in case smoker is too tough for you to consistently farm at the moment). Generally levels that have a "known" boss at the end and also have lots of stages to them will give best experience rate. Hope this helps and sorry for forgetting the amount given for stage 10 on twin capes.

Edit: Also just found out from a question I was asking on forum for a different matter that the turtle island event (granted that is extremely infrequent and not an actual exp "farming" possibility) gives better experience than the 15 stamina arlong event at 1250/15.