From the photos, the sunrace shifters look to have an awfully small clamp for downtube. I think they're mislabed and are actually stem shifters.
So depending on if your stem is quill or threadless will make the descision for you. Since the sunrace needs a quill, and the shimano ones are basially threadless stem shifters.
Both are pretty low end though, I'd check ebay for some quality used items first.
or get 2 of the sunrace shifters; throw away 1 lever from each, bolt them to the tips of your drop bars as 'poor mans' bar end shifters.