I've tried out three premium backup services, having a paid account for a few months with each of these three services.
Mega.co.nz
+ No filesize limit, encrypted uploads, very professional design.
- Expensive, encryption keys can be sent to Mega although I don't think they're doing this (yet). No FTP, remote upload, etc.
1Fichier
+ Cheap, speeds are decent
- Translations are bad, the site looks like it's from the 90s but the service is actually quite decent. Unlimited storage? Probably not but I never had issues storing over a few hundred GB.
File1.info
+ Cheap, remote upload, FTP upload, hotlinking and sick speeds. I'm maxing out downloads to a seedbox at around 600 mbit/s (60 MB/s). 1TB hotlink every month included.
- No unlimited storage
Basically all three are good, I really like how mega looks but it's way too expensive for me. 1fichier looks like crap but it's very cheap. Currently I'm using file1.info because it's the fastest in Europe, looks great and is cheap.