We stayed in Carlsbad at the Residence Inn to be near Legoland on a recent trip. We also went to Sea World which was about another 25-30 minutes down the I-5. Our Sea World excursion was on a Saturday--I'm sure it would take considerably longer on a weekday with traffic.
It was fine for our requirements which include needing a separate room for the kids (it was a 1 bedroom suite), being acceptably clean, though it wasn't spectacular in that regard, and being fairly inexpensive ($95/night). That also included parking, free breakfast, internet, and they had a free shuttle to legoland. I'd also add that it's in a super quiet area and was not very scenic. There was a small pool, a hot tub, and a grill for guests to use.
Hard to say if we'd stay there again, mostly because we'd probably focus on the zoo the next time we go down and pick someplace closer to that area and not because there was something in particular about the hotel we didn't like. It just wasn't that interesting, but was a fair value.
We also had lunch at the Sheraton next to Legoland. That hotel had a very nice view, the lobby and pool area were beautiful, and the staff seemed nice. I can't say anything about the rooms though. We might be interested in staying there, but we'd need two rooms which would make it a bit pricey.
