technicsplayer: yes, there are latency issues depending on the audio drivers of your computer whenever you use soft-synth-based programs like Reason. These can range from over 400ms to less than 8ms. Windows audio drivers have improved and can provide very low latency.

jetgraphics: just FYI, in your original post you used the word "arranger" in relation to Reason. Just so you know: in the context of this group this word means "auto-accompanyment", as in a keyboard or software program which can produce bass-chords-rhythm backing based on live chord input and can change with that input. None of the programs you've mentioned can do that, and in fact there are very few software programs that can (I've seen very few anyway). All of the programs from Reason to Band In A Box can produce "arrangements" of songs, but they are basically sequencers and cannot do what "arranger keyboards" can do.