I prefer The Speaker as well. I think it has more interesting characters and the plot is more complex and compelling. The Speaker is technically a prequel, so it's fine to read it first and then decide later if you want to read the Dear series. The only tie between the Dear volumes and The Speaker is Ryuu, a young man who worked with the trio from The Speaker. Even then we only get a few panels of the Speaker trio in the Dear series and it's only to vaguely fill in Ryuu's backstory. So not a big deal if you skip out on the Dear series or vice versa.
is it ok if im only interested in THE SPEAKER? idk but the volumes before it dont really interest me much. do they have so much connection? if its no trouble i hope someone can help with briefing :D