I've owned a 1648 (which I sold to another member on this forum) and now own a 1652. Both cab. The 16xx series is the previous, tier 3 models. These tractors are built in Japan, for AGCO (parent company of Massey, one of the largest farm companies in the world) by Iseki manufacturing. Have been for a long time. They are top notch machines. My series machines have Iseki built diesels (great engines) but for Tier 4, the 1758 comes with a Mitsubishi diesel. No worries there, Mitsubishi builds great engines. (I had a Mitsubishi in my LS, and also currently have a "Perkins" branded Mitsubishi in my Terex track loader.
My 1648 was flawless except for one small thing. Right around 550'ish hours one of the hydraulic lines developed a fitting leak, which was promptly fixed under warranty.
My 1652 is right around 560 hrs I think... Also flawless. I work it hard for my landscape company. I am extremely impressed with the quality and durability.
I've also owned Kioti and LS. I have direct experience with the competing Kubota models and some JD models. The Kubota's are nice also. However, in my experience, the Massey (Iseki) machines are more durable and reliable.
I will say that the loader valve on the Kubota is better... You can feather dual function (boom and tilt cylinders at the same time) more easily on the 'Bota. They also now have a throttle-toggle on the loader joystick (the grand L series) which is neat. Kubota also offers a "dual" 3-range HST, which gives you a Hi-Lo in each of the 3 HST ranges, effectively giving you 6 HST speeds. That's a nice feature, though my Massey HST is never wanting for power.
The MX machines are nice too... Somehow Kubota bills them as a "utility" tractor even though they offer less strength and features than both the Massey 1758 & Bota L6060.
Bottom line, you probably can't go wrong with either one, shop by preference. Good luck!