I have owned both and can say they all have their good points. The one camera I truly regret selling was my yashica mat 124( and my M3 doublestroke). The Mamiya TLR's are great also, I had a 330 with the paramender etc. What I found I didn't like was the 6x6 format.....it just didn't work for me yet I have seen many others that do stunning work with it...I'm just challenged I guess. SLR's are great too but you are going way up in price, especially for a hassy. If you are not sure about moving up to med format try getting a good Yashica mat 124($200) and experiment. If you don't like med format it will still be worth the $200 when you are done. I would also suggest finding an inexpensive 6x9 folder these can be great camera's and the 6x9 is the same ratio as 35mm just a way bigger neg.