If quality of light is important then USAI. BeveLED Mini is a good option for transitional and is diurnal so you can adjust the color temp or have their software or your HA system adjust it during the day. They have very uniform color fixture to fixture so you don't have problems of some being warmer or cooler than others. They are also 92 CRI.
For contemporary or transitional I'd think you'd want 2" - 3" aperture. 3" - 4" works well for traditional architecture. 5" - 6" is quite big and typically makes a house feel dated. Square vs Round is mostly an aesthetic decision though square are only adjustable in one direction which is kind of limiting so I use round unless the ceiling pattern requires square such as beadboard.
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Linear pendant over island
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