I'm not an installer whereas many in this forum are. So I don't intend to cast any aspersions with these comments. I feel that many installers have an agenda, either their own, or one imposed by the company they represent. Hopefully you will get an installer who can answer your questions accurately and honestly, but how will you know? One defense is to arm yourself with as much information as possible, from sources like SG and discussions with other techies. Then ask several installers the same series of questions and weigh their answers. In your case I would definitely be asking which sat. carries, or will be carrying, your HD locals. As I said before, that will probably make your choice for you. I'd also ask, it he were doing the installation for himself and could choose the "best" option, which would it be and why? Your exact location may have a bearing, particularly if you don't have line-of-sight to one or more of the sats. If you do have LOS to 129, would a separate dish, perhaps a larger one work better? Or would you be better off with a D500 for 110 and 119 and a separate D300 or D500 pointed to 61.5 (again assuming LOS)? Get answers to these questions and consider the responses. The fact that you know something about the situation will hopefully guide the installer to giving better answers. Perhaps he may even have some flexibility as to what he can/will install.
In general what's considered "best" is what will work reliably for the lowest cost. That may not be optimal, tho'. Caveat emptor, and YMMV...!
