You'll find supporters and detractors of both services. My personal opinion is that Bell offers a superior product, in terms of channel selection and especially HD selection. I've read recently that Shaw has added more HD channels, so the availability of channels on each service is likely more similar now than in the past, if not the same.
Bell (via Dish Network in the States IIRC) has new MPEG4 HD receivers in the pipeline, which means more HD channels should be a possibility soon. But the old receivers won't work with this compression, so I'd be leery aboout buying a Bell HD receiver now without some serious thought and investigation.
Bottom line - avoid Telus TV!