I've been using mixture of contractors based on best price and sometime on convenience. Most of the time using their panel of sub-contractors would make things go smoothly and they already have mutual expectation. When you introduce someone unknown to them, you'll have to be the middle man and get them talking to each other. I'm lucky that they communicate and don't need to escalate to me for solution. My main con do not push his sub-con but instead ask them to fight for the job based on best quotation. Here is my list

- electrician - main con panel - lowest price among 3
- aluminum sliding door - main con panel - convenience since he supply the windows as part of main con deliverables
- plaster ceiling - main con panel - convenience since he supply ceiling as part of main con deliverables
- tiling - someone else - lowest price among 3
- painter - main con panel - lowest price among 2 plus better workmanship
- grills & gate - someone else with better quality but medium pricing