it really makes sod all difference what people use as long as:
-Its a recognised device
-The belayer knows how to use it correctly and has experience with it
-The climber is happy being belayed by that belayer on it.
Personally i always use a grigri for sport climbing or at the wall as i find it a bit more 'relaxing' to use for a full day of climbing, and its much better than a standard plate type device if the climber is working a route and having lots of rests.
For trad i'll use an ATC XP as i tend to climb on skinny doubles.
Theres always going to be climbers arguing the pro's and cons of each device, but as long as both partners are happy with the set up theres no point worrying / arguing about it.
Same goes for abbing, ive abbed on grigris and ATC's, as long as you have tried the device in a controlled situation and know how it feeds through on the ab theres no problem. I nearly always back up with a prussic though as it means you can take you hands off to sort out rope tangles, and it makes things feel less intimidating on free hanging abs (well to me it does)