My suggestion simply from a financial perspective is do not rent to own...alot of the money goes to interest (as in any loan) not to the instrument. If money is tight a used horn might be a better choice for right now, plus you would have more options than just Conn/Yamaha within any given price range. However to answer your question there are several options
Conn 6D and 8D
Yamaha 567, 667, 667V, 668
I would NOT recommend rent to own for a Conn 6D or Yamaha 567. These are both intermediate models and if you become serious about music will need something better, probably about the time you finally finish paying off the loan. These would however be great instruments to buy used. Assuming you kept them in the condition you purchased them, you could probably get back most of your money selling it when you decide to upgrade.
The Conn 8D and Yamaha 668 are very similar horns, both large bell and available in nickel. Between those 2 I would go with the Conn, they are common, well built, and easy to sell used.
The yamaha 667 and 667V are a very different playing style than the Conn. The 667 has a much smaller bell throat, which gives it different playing characteristics. Those characteristics however are a personal choice. (I actually switched from a large nickel horn to a 667) There is a good market for used 667s (more so than the more expensive 667V, the 667V really isn't worth the extra $$ over the 667 in my opinion) and there are also several repairmen that will tweak factory 667s
So if you rent go with a Conn8D or Yamaha 667, but those are very different and which one you choose is a personal playing style choice. However I still strongly encourage finding a used instrument you can afford and buying it outright, from a financial standpoint that is FAR superior to any rent to own and will give you more time to find out what's out there and what kind of horn you really need before you purchase a truly professional model.