[Phalanx]

None of my animals have had a HUGE shelf life unfortunately.
The cats, probably on a record here, I've had one of 'em for 5 years, one for about 3 and a half.
Dogs?
The top two would be
The dog I grew up with, Ned. German Shepherd x Cattledog. 3 legs but could still outrun me way too easily. He was with me from birth until I was 12, and with my family 2 years prior. He was fairly old, but yeah...he'd already lost that leg to cancer, it was kind of a recurrence elsewhere in his body.
The other would be Loki, who was poisoned last year. Had him from around 15 to 24...He was getting on in age, but would've lived another 3-4 years easily. To this day, the search continues for his (among 30+ other pets) killer, in the town he was baited.
I hold both those dogs at "favourite" status...they were friends through big stages of my life.

However, the loss of a pet can effect you after a shorter time...always hard...I've not had a human death close enough to effect me personally so I'm not sure what it's like in comparative terms...but it's a terrible thing.
I've said this before, and will again...this experience is a price you pay as a pet owner, you pay this in exchange for friendship and (in most cases of being a "good" owner) loyalty, the time you spend together. Is this a fair exchange?
I can never say that for anybody else...but in my case, I'd say it were worth it. IMO, If you suffer for the loss, then you know the time was well spent.