Bottom line, there is no Marriott brand hotel in Hollywood, you will have to drive there no matter where you stay. Realistically, you're not going to see a celebrity in Hollywood. You're just as if not more likely to see someone famous walking down the street in Santa Monica than you are at a tourist site in Hollywood. The WB Tour will at least let you see sets, just keep your eyes peeled for people walking and driving around the lot. If you're worried about driving time, use Google Maps to check the distances between hotels and the places you want to see. You can see the walk of fame, Chinese Theatre and Hollywood sign all from Hollywood and Highland. It should be a tour stop for every Hollywood tour. Check with the Hollywood chamber of commerce, there may be a star unveiling ceremony while you're there, so you could plan to go see that.
Personally, I'd probably pick the Marriott in Santa Monica that is about a 2 block walk to the beach and a few more blocks to the SM Pier. It's a short drive to the far end of the 3rd St Promenade, where there's 90 minutes free parking and then $1 per hour during the day in city lots. The closer end of the promenade and the SM Place mall are walkable, but also have city lots. The Starline (or Grayline, not sure which) hop on, hop off bus also stops there, so that could be another option for getting to Hollywood Blvd.
If the priority was going to Hollywood multiple days, Sherman Oaks might be closer, but I don't know that area as well, which is why personally, I'd pick the beach. If I knew for sure there'd be a red carpet premiere at LA Live, then the Marriott there might be a good choice, but again, not a priority for me, so I wouldn't know a lot about the logistics.
