brsboarder

My beloved Giant OCR 2 from 2007 was stolen and I need to replace it. I use the bike predominately for a short 15min commute but want to be able to do a weekend ride in a group.
Unfortunately money is tight so I'm looking use and the market in my area isn't great.
My max budget is ideally 800.

I am looking at:
2019 Cannondale CAAD Optimo for 700
2015 Specialized Roubaix SL4 in like new condition for 900
Giant escape 3 for 450
Trek Pilot 5.0 Domane (unsure year) for 900

Iride01 

Out of all of those bikes, assuming their sizes match, the Roubaix is designed to give a more relaxed or upright position and has quite a bit higher stack than the others. So if you prefer a more relaxed geometry that's probably the one. Otherwise, depending on what the actual sizes are, the others have a more aggressive geometry with less stack, so you'll be more aero in position.

Couldn't find the specific geometry for your OCR 2 from 2007, however it appears to have a stack that would put your body position less upright than the Roubaix, but more upright than the others. Though again the sizes matter for the stack height. One size difference in the same model can change the stack height quite a bit.

If your budget is tight, then make certain that everything works with those components. You can quickly have a money pit if certain components need replacing and they also require replacing other good components that aren't compatible with the new.