Bleach is the longest ongoing series I'm watching with the intention of finishing, Series 1 was the first Anime set I bought back in 2010, needed to buy from Series 9 onwards for a good while which I finally did earlier this year (going through Series 11). I'm still only on Episode 170 at the moment. Have read the Manga up to date with volume releases though!
REBORN! and Gintama are probably the next longest series I've been watching, they were the first shows I started watching when I got a Crunchyroll Subscription sometime Early 2011. At this point I've made it to Episode 153 of REBORN! and I've watched a paltry total of 17 episodes of Gintama, not sure I have the desire now at this point to get back into it!
There are a few others knocking about on my On-Hold list for a good few years, in terms of actual completion at the top of my head Air Gear is probably the longest, if I recall it took something like 15 Months to finish.