Well... You asked for it...
The 2nd gen Frontiers run from 2005-now, with a replacement coming soon on the horizon. They are absolutely fantastic trucks, and a good alternative to the Tacoma. Great thing about them is they can be had for much cheaper than an equivalent Tacoma. Around here, the difference is around $3-5K, depending on the truck.
Similarities:
Both are about the same length, width, and height, with similar size beds, similar wheelbase, similar approach/departure angles. They are a similar weight, both have 4.0 V6s, both can be had with a 5 speed auto or 6 speed manual, both have cool off road packages, reliability is just about the same, and parts availability is similar.
Differences:
Engine - while they are the same displacement, the Nissan VQ40 is more powerful, with 265hp/285lb-ft.
Interior - the Nissan interior is nice, but a bit more utilitarian than the Toyota. It's still a nice place to be though. The Nissan feels more like a truck to be in, with a more upright seating position. The Nissan also has a quite a bit bigger back seat. If you're a bigger guy, the Toyota seat can be adjusted a lot more, but I've never been uncomfortable in my Frontier. The Frontier dash layout is nice and there is a ridiculous amount of storage inside. Giant door bins, a cavernous center console, and two, yes two, glove boxes.
Ground clearance - the Nissan is more low slung. The result of having a more upright seating position is a bigger cab, which hangs down lower than the Toyota body. The frame heights are actually pretty similar, but the Toyota body is more on top of the frame, while the Frontier sort of wraps around it more if that makes sense. As a result, the Nissan is noticeably lower. My truck on 33s and a 3 inch lift has only about 2.5 inches more clearance under the doors than my friend's Tacoma at stock height. Don't get me wrong, the Nissan will definitely go all the same places as you can take a similarly modified Tacoma, but you'll be using more armor.
Suspension - the layout is similar, with coilovers on the front and leafs in the rear. The rear is just about the same, just with different axles. The Frontier rear axle seems to be a but more heavy duty than is necessary (which is a good thing), as the manual and off-road versions sport the same Dana 44 variant axle as the V8 powered Titan. The other axle isn't quite as beefy but it's still plenty tough. They both can take a lot of abuse. The front is a bit different. The front suspension places the UCA over the coilover instead of outside it. Also, the frame is wider than the Tacoma's, so the control arms are shorter. As a result, the Nissan doesn't have as good of suspension travel as the Toyota does. The design is still very good, but the travel is more limited. The front differential is not as strong as the Tacoma's is, but unless you are running 35s or doing a lot of tire spinning, it's not much of an issue. The front suspension can be upgraded for pretty cheap, since the Titan and the Frontier use (roughly) the same frame. This means you can bolt Titan suspension to a Frontier. That gets you into a long travel setup for pretty cheap (comparatively speaking). You can also bolt up the stronger M205 front diff from a Titan.
Frame - the Frontier has a beefier, boxed frame versus the Toyota's c-channel frame. Whether that makes much of a difference is a matter of debate. The Frontiers don't have a frame rust problem like many of the Tacomas do.
Fuel economy - on average, the Tacoma will get slightly better mileage. The diffence isn't super dramatic, and that gap can be closed a bit with some minor mods, but it's there.
Aftermarket - this is where the Toyota has the largest advantage. The Tacoma has many more options for bumpers, sliders, and suspension than the Frontier. That being said, the Frontier has all the necessary stuff available. ARB, Shrockworks, and Hefty Fab all sell front and rear bumpers for it, and there are a few companies making skids for them. Sliders are also easy to find. The Tacoma has many more suspension options, but the Frontiers still have enough. OME, Radflo, TJM, and a few others make suspension parts for it, so you've still got plenty to choose from. Otherwise, the Frontier is pretty well represented.
There's not too much to be concerned about with these trucks. 2005-2008 had an issue known as the strawberry milkshake of death, where a trans cooler line that goes through the radiator would crack and and the trans fluid and coolant would mix. This would take out all the seals in the transmission and cost you about $5k to get a new one. Luckily, this problem is pretty easy and pretty cheap to get around, and if you want to avoid it completely, the 2009+ trucks are cured of the problem entirely. Beyond that, the minor headaches include a belt tensioner that isn't as long-lived as it should be, and a squeaky hood latch. Luckily, both of these are really easy and pretty cheap to fix.
Otherwise, they're damn near bulletproof. I cannot overstate how reliable and capable mine has been. They're whisper quiet on the highway, they're comfortable, handle well, accelerate well, off road well, and look cool. They're really great trucks both on and off the road. Mine has been an absolute pleasure to drive, and it's never let me down. I do really like it more than the Tacoma. I like the looks better, the price is much better, and then there's the fact that it's so different. Modded Tacomas are pretty common. Modded Frontiers are not. It's cool to have something not as mainstream.
I would buy another one in a heartbeat.
