Well engine and power wise they are the same. The L3800 looks like it has more of a sleeker design, almost closer the the Grand L's. The SU in the L3700 is supposed to mean Special Utility Tractor Loader. I think this means that that it is really made to come with an FEL and BH. But otherwise i am not sure either, i had the same question.
The 3700SU was made to compete with the budget Deere. From what I've read here, its going to be a one year only tractor. The L3800 is a bit updated, even if it's mostly sheetmetal. You will probably find the loader a bit better on the 3800, but the two tractors are pretty comparable.
I have the 3700SU. I looked at both the 37 and 38, you get a better loader and updated sheet metal with the 38 and a jump in the price. The deal was to good on the 37 TLB,thumb,loaded R4 rears, skid steer front. For 26000 something. I have had it for 6 months and the only issues are the jerky 3point, and the BH is cramped for me at 6'2". I had a BX22 that had more room when using the BH.
Tomtint, I agree with you on the tight BH, a friend has the same unit as you, but paid a lot more, but I'm just shy of 6ft, and 220, and I don't like the operaters platform set up on the L3700, would be nice, if they would put the swivel set set up, like my B3200. I also fit on the BX 23 BH better.
Someone pointed out that the L3700 didn't even have a suspension seat. That would kill it for me... I just assumed the L3800 has one... can anyone confirm that?
Myself and someone else spent about 6 or 8 post trying to convince a new L3700SU owner that, yes he had a suspension seat, he just did not know how to adjust it. Finally the new owner took some Pics.. guess what? no suspension seat! I felt bad kinda bad about that.
James K0UA