Prefer T-I Jazz Flats, but always keep one Alembic strung with T-I Jazz Rounds. No experience with Rotos, but like Paul said, if you like 'em, go for it.
One thing to bear in mind, on a long-scale Alembic, there is still some afterlength of string behind the bridge to account for... make sure the set you're using will reach. As you're also about to discover, changing strings on our Alembics is a snap... a 5-minute job. Good opportunity to tweak the action/intonation too.