I'd second
Hermes ' sentiment. The riding from downtown itself is pretty poor, it will take you a while to get to open roads. I find going north to be much more scenic and you have access to Fiesta Island and Mt. Soledad which are great for interval work, but it will take you ~20 min of riding (prob 25 elapsed b/c of intersections) just to get up there. If you can increase your ride time a bit I think it would be worth it, otherwise I'd stick to the hotel bike.
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"Your beauty is an aeroplane;
so high, my heart cannot bear the strain." -A.C. Jobim, Triste