Dunu Titan S vs Tin T3 Plus vs NFAudio NM2
So, I somehow ended up with all three of them and they are all contending for the "best under $100" tag.
I will just do a swift ranking. Also Aria is not here as I have loaned it to someone but it will be put in the comparison as well for reference.
Build: Titan S = T3 Plus > Aria >> NM2
Titan S with their metal shells and T3 Plus with the resin shells - both have excellent build. Aria's paint tend to chip off and NM2 has the build quality of $5 QKZ IEMs.
Accessories: T3 Plus = Titan S > Aria > NM2
T3 Plus got a good cable and decent tips but the carrying case is poor. Titan S got a great carrying case (better than many expensive IEMs come with) and good tips but meh cable. Aria got horrible cable and meh eartiops and case. NM2 got the worst accessories of the bunch, replacement recommended.
Bass: Aria = Titan S > NM2 > T3 Plus
Aria has slightly denser bass whereas Titan S has more "neutral" bass tuning. Both are fast with good texture. NM2 can sound lacking texture in mid-bass at times and T3 Plus lacks texture.
Mids: NM2 > Titan S > T3 Plus = Aria
Both T3 Plus and Aria have issues with lower-mids. NM2 handle lower and upper mid pretty well, so does the Titan S. However, Titan S tended to get slightly shoutier.
Treble: Titan S > NM2 > T3 Plus > Aria
Aria has the weakest treble response among these. T3 Plus has a bit more energy in lower-treble. Titan S and NM2 both got good treble extension but the NM2 has more focus near lower-treble which can be fatiguing. If you like higher amount of treble: NM2 for you.
Soundstage: Titan S > Aria > T3 Plus = NM2
Perceived stage is widest and deepest on Titan S. Aria comes second though the margin between Titan S and Aria is sizeable. T3 Plus sound congested, whereas NM2 can sound too forward at times.
Imaging: Titan S > NM2 = Aria > T3 Plus
Separation: Titan S = NM2 > T3 Plus > Aria
Dynamics: Titan S = Aria > NM2 > T3 Plus
I am bit torn here. Microdynamics are superior on Titan S whereas Aria has better macrodynamic punch (e.g. sudden bass drops).
Overall, I think the Titan S ticks most of the boxes. It's got good technicalities coupled with a neutral bright tonality that works well. NM2 is the most technical among them and will cater well to those who need more information up top.
Aria meanwhile got the best timbre and has the smoothest signature here. T3 Plus is more of a mixed bag due to the odd-sounding bass.
I'd probably pick either Aria or the Titan S for my personal use. They complement each other well so one can even have both and not feel like they bought similar things. NM2 remains something I like listening well-mastered tracks with, though cable change is a must. T3 Plus is mostly useful for commuting, not so much for critical listening.