Rucu Pichincha is an easy hike for acclimitization on the outskirts of Quito. You basically get a ride to the gondola (TeleferiQo sp?) and hike to the top with a little easy scrambling toward the end. If you have a guide and/or your own transportation, Guagua Pichincha is more interesting with more opportunities to explore and walk around all day at moderate altitude. There are some other moderate peaks outside Quito that could also be used as alternatives including Fuya Fuya (~14k ft), Imbabura (~15.1k ft) and Pasochoa (~13.8k ft). HIking around Cuichocha Crater would make for a nice afternoon which is around 11k ft. All of these are here on SP. Personally I haven't climbed Illiniza Norte, but I'm sure it would be a good peak for acclimitization, but I understand it can be a little crowded, and probably best done after tackling a smaller peak first.

Chimborazo is hard, nasty and potentially dangerous depending on conditions. I had very hard blue ice when I did it a few years ago. I liked Cotopaxi and Cayambe much more, so if you want to climb the highest peak in Ecuador and are up to it, fine. If you'd rather have a more enjoyable and interesting climb, I can personally recommend Cayambe. Antisana is also likely a nice alternative and is much less popular since there's no hut and you start by going through private property. I would check recent conditions before making a final decision. I have no idea what is going on with guides or huts currently. I'm sure there are others on SP who might be able to help you in this regard.

Woodie