| Hi,
I'd order the same size that you do most of your jazz playing on. The "J" stands for "Jazz" and the "J" slides do some cool, slipperier "thangs" to bend notes and such.
For me, that would be to go with the J1 first. If you play a lot of lead on the original #1, consider the J4 also . . . it's a tad brighter edge to it, if that's what you like.
Tom |