Since you have had such a memorable and happy tenure with your R15S, you could consider a brand new MT-15 as a replacement since it has ABS, more upright and comfortable ergonomics and uses an engine that you are intimately familiar with.
Another option you could consider is either of the Suzuki Gixxer 250 models, depending on your styling preferences. The Suzuki 250s are solidly built, have punchy performance and will return decent fuel efficiency as well.

