There are a few differences in the Yukon and the Rincon. First is the fork, the Rincon has an SR XCM fork and the Yukon has the Rockshox Dart 1. The rest of the components for the Rincon are:
shifters Shimano EF50
front derailleur Shimano M310
rear derailleur Shimano Alivio
brakes Tektro I.O. Disc
brake levers Shimano EF-50
cassette SRAM PG820, 11/32, 8-speed
chain KMC Z72
cranks SR XCT, 22/32/42
bb SR Cartridge
rims Alloy, Double Wall
hubs Formula 32H Disc
spokes Stainless steel
tires Kenda Nevegal (silver/black) /K-Rad 26 x 2.1(black)
handlebar Alloy, 31.8mm High Rise
stem Alloy
seatpost Alloy 350x30.9mm
saddle Giant Unity SpeedGroove Plus MTB (Anthracite/Black) & Giant DJ (Olive/Black)
pedals Alloy Platform
For the Yukon they are:
shifters Shimano Alivio Rapidfire
front derailleur Shimano Altus
rear derailleur Shimano Deore
brakes Hayes MX-4 Disc
brake levers Tektro Alloy, 2-Finger
cassette SRAM PG820 11-32, 8-speed
chain KMC Z72
cranks TruVative ISO Flow 3.0, 22/32/42
bb TruVativ Powerspline
rims WTB Dual Duty, Double Wall
hubs Formula 32H Disc
spokes Stainless steel
tires Kenda Nevegal 26 x 2.1
handlebar Alloy 31.8mm, High Rise
stem Alloy
seatpost Alloy 350x30.9mm
saddle Unity Speed Groove MTB
pedals Alloy Platform
The front derailer on the Yukon is now the Altus series, they say it is a Acera, but they changed it due to some shifting problems people were having.
Here are the Trek 4300 specs:
front fork RST Gila T8 w/preload, 100mm
Wheels
Wheels Shimano M65 disc hubs; Bontrager Ranger rims w/eyelets
Tires Bontrager Jones ACX, 26x2.1"; 27 tpi
Drivetrain
Shifters Shimano EF50, 8 speed
Front Derailleur Shimano C050
Rear Derailleur Shimano Alivio
Crank SR Suntour XCC-T102 42/34/24
Cassette SRAM PG830 11-32, 8 speed
Pedals Alloy ATB
Components
Saddle Bontrager Race Lux Basic
Seat Post Bontrager SSR, 20mm offset
Handlebars Bontrager SSR, 25mm rise
Stem Bontrager SSR, 10 degree
Headset VP-A76C-TK, 1 1/8" semi-cartridge, sealed
Brakeset Shimano M415, mechanical disc w/Shimano EF50 levers
As you can see the 4300 is closer to the Rincon, just more expensive. The 4300 and the Rincon share alot of features, like the crankset and the brake/shifter assembly it is all one part, where the Yukon they are different parts. The most important factor is that you enjoy riding it, and that it fits you.