I use both. I LOVE my bottles for outlining,flooding, and sometimes writing. I really didn't think I'd be able to write with bag, but actually it's not that hard. If I have really thick icing to do designs with tips, I use bag. To me bottles are easy to clean, pop them in the dishwasher. But I clean my tips by hand. Also with the bottle, if you'e got thick RI or TG, then you can thin it down right in the bottle. I have some bottles with the big neck, those you can't change out tips. My favs are the small bottles that can change out tips.
As for filling, I just kind of hold up my thicker icing in spoon, let it drop (like teardrop) in the bottle. If it's really thick, I squeeze the bottle, spoon some icing into the top and unsqueeze the bottle, it sucks the icing right in. For flooding TG, it just pours right in.
I know you all know TracyLH using only bags, I don't know where she gets that control and steady hand, but her cookies are amazing!
Shiney
Take a picture; eat the cookie!
Shiney
Take a picture; eat the cookie!