the 188 is a great all-around tuba, especially if you're planning to do more large ensemble playing than small ensemble playing. the 188 will work very well in large ensembles but will also play light enough for quintets and such. if you're doing more small ensemble playing, I'd lean more toward the old 186's (I don't like the new ones much) or even better, an RM-43. Both of those horns will keep up very well in large ensembles, but they're leaner sounding & more agile for the smaller stuff.
-ck