The question of what secondary to use, is like asking what car we bought. You will get many different answers for sure, but is still a good question.
Plastic food grade buckets are fine. Lightweight, prevents direct light from entering, easy to move because of a handle, and is not fragile. Very cheap to buy. But, they can become discolored, and contain odors from prevous batches. And taking samples are harder as the lids snap on nice and tight, and can be a struggle to remove, and the wide opening can allow for accidental contamination when the lid is off. They can scratch easy when cleaning...but again, they are cheap to replace.
Better Bottles are fine as well. Lightweight, easy to move around, easy to clean, prevents oxygen from permeating, and is an anti-wetting type container. You can buy with or without a spigot, and have different sizes. Not too bad a price either. Easy to remove samples. The do however allow light to penetrate, but a t-shirt, towel or carboy cover can be used.
Glass carboys are just fine as well. Easy to clean, prevents oxygen from permeating, does not discolor, and will not contain odors from previous batches if cleaned correctly. Relatively cheap to buy, and easy to remove a sample. They are heavy, and can break, creating a huge mess. They allow light to enter, but like the Better Bottle, can be covered.
Conical Fermenter...yeah! Used as a single fermentation chamber, with the ability to allow removal of trub, yeast, and samples. Prevents light and oxygen from entering, and are easily cleaned. But, they are very expensive, bulky, and take up more space.
Choose your seconday according to your planned use. I use 5 gallon glass carboys myself. But I will admit, I am always worried about mistakes and breakage, and work with much care around them. I bought them...because my LHBS had them cheap.
If I had the cash and the space...I would buy conicals. But, I have buckets, and glass carboys to use, and would definately use Better Bottles if I had them.