Welcome to 3 Wheeler World Clvasko!
Sounds like they would both be a good choice. Without taking price into consideration I would be leaning toward the 4-wheeler.
The quad gives you electric start and reverse, both very handy and unlike other quads it will turn just as well as the trike (probably better in mud). The biggest downsides with trx125 that I have found is that it's small in size (I am 6"2") and slow. Size wise it's not too bad unless you plan on a longer ride. Power wise it's good, not as much as the 200 but still good, it just doesn't have much of a top speed. I have owned 2 Honda 200s’s and have a fare amount of seat time on a friend’s trx125, I have more fun on the 200s but I have been impressed at what the “little” 125 can do.
If you or someone else will use the ATV for "fun" (more sporty riding) then the 200s is a better choice.
But like I said before I think both will work well for what you want, just make sure they have good meaty tires.
1984 Yamaha YT 60 Tri Zinger(current project)
1983 Yamaha YTM 200 (rear suspension kit)..... long term project
2004 BMW R1150R
1972 Honda CT 70
2007 Lifan 110