I went from a Frontier to a Titan, way back in 2004. I had a first-generation Frontier (98KC with every option, 5 speed) and I loved that truck and it was cool looking. But the Titan kills it in terms of space, which was a major issue for me with 2 big dogs at the time - and the flat (virtually flat) floor in the back of the crew cab was a clincher for me. I missed my stick, but the Titan's drive train is the best of any vehicle I have ever owned, and I've had a lot of vehicles. So smooth and so much damn power.
A few years back I sat in another first-gen Frontier (about a 2000 model) KC and I remembered something I did not like, and that is the same complaint I had with my 2001 Pathfinder - not enough shoulder room. I have pretty broad shoulders (46" chest) and my left shoulder was always jammed into the pillar. On the Titan I swim in the seat. It's nice -really nice.
About 2 years ago, I went and checked out the "new" Frontiers to see how they were for interior space, since my Titan was starting to get long in the tooth in miles and I was considering whether I wanted to replace it with something a little smaller. I felt cramped in the Frontier and even in the crew cab the floor space in the back seat was disappointing. I use my Titan with the back seats flipped up almost all the time, and though I am driving a crew cab and you're looking at a king cab there's a good amount of space back there too.
As for quality control, my first generation Frontier had zero problems, so the Titan has not been as reliable, but I've never had any totally serious problems and never been left on the side of the road. I've had to be a little more of an active owner - my Frontier was just drive and forget it, nothing ever broke - but it hasn't been overbearing, and the tradeoff for the extra space and comfort is worth it to me.
Personally, I think you'd be happy and in a couple of years wonder how you ever did without it. One caveat - make sure it fits in your garage, if you have one and use it. My Titan fits, but if I got a long bed it would be crammed in there pretty tight. If you need the longer bed, you know they make a crew cab with the full size bed?
PS: Before the Frontier I had a Nissan Hardbody that I also bought new. Was totally trouble-free but really crude compared to the Frontier, forget about compared to the Titan.
