Some of the Citi ThankYou Premier cards have an additional 10K points after $12K annual spend. If you have a pile of flight points with that card as well, you could theoretically get (based on $1K rent): $12,000 x 1 TYP + 1 FP + 10K points = 34K TYP. I realize this earning is based on a lot of factors you may not have, but it's the only other option I see to get the highest point total from that spend. Almost all other annual spend requirements are $20K+
Now, some people might argue that 12K or 18K United points are worth more than 34K TYP, but that depends how you value each point.