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It depends on the kind of hotel.

If it's a chain hotel, it's best to book with the chain. Many chain hotels these days only give free internet to those who booked through the hotel chain website, for example. Plus if there's any question about the reservation, it's better to have only company responsible for it, as opposed to a booking site telling you to go the hotel program and the hotel program telling you to go to the booking site when there's a problem.

If it's an independent hotel, I prefer booking.com because they have verified reviews and because on their site you can print a confirmation to show the hotel in the hotel's local language. I don't know of another site that lets you do that.

For reviews (especially of chain hotel properties whose quality you're unsure about), you can look at TripAdvisor, but remember to ignore the very best and very worst reviews (as those may not be valid reviews); ie, don't use the score, read the reviews, and focus on what features of the hotel you're interested in while reading the reviews. For example, if you care about breakfast, "breakfast was good' from one person and then "breakfast was lousy" from another person is useless, because you can't tell what their standard was. On the other hand, "breakfast consisted of A, B, and C" (if you can find such a review) is much more useful.