I agree with others that say buy as powerful as you can afford to now. However, consider what your needs are also.
In my case I did not need a 34hp tractor but felt uneasy on the smaller frame tractors due to my rolling hills. A good deal came along so I jumped on the 3430 after shopping for over a year.
As to needs, if you dream of clearing a horse barn out with the tractor (or something else with limited space), be sure to do the measurements. I had to give up easy access to my barn with the 3430. However, we had planned to change the doors this summer and that will fix that issue.
I love my 3430HST. I am sure you will be happy with which ever of those three tractors you decide on.
Don't just shop the size, shop the tranny also. As a neubie, the HST is worth it's cost to me!