I've always considered the, "Where should I sit at a ball game?" question to be very individual.
Safeco is a quality modern yard, you'll get good views from nearly all seats. I've sat on the 1B line, the 3B line, overlooking LF, in the seats behind RF, I've always had a good view. If the roof is open, sitting in the upper deck on the 1B side will provide a pleasant view of DT.
I'd say sitting in the lower bowl - including behind RF - generally equals more avid fans, more chance of feeling like you're part of some energy.
Re: hotels, again, depends what you are looking for. Staying within walking distance of Safeco is pricey, I personally would say it is not at all worth it. There are places DT, north of Safeco (as in near the convention center), which are only a short bus ride away, that are much less expensive, and closer to interesting shopping/dining/sightseeing etc.