I think your size might help in make up your mind, I'm going back to a 125 coming off an '03 YZ250F. Things I don't like about the 250F it's big and it feels big you can feel it's top heavy. I hate the engine braking even with the auto decomp cam it's still hard to start sometimes a major pain if you dump it over hard. Its definetly not flickable like a 125 especially if your vertically challeneged. The bike just beats me up and it takes more energy for me to go fast on it. It's a great bike no doubt, you may ride one and like it or hate it if you like the light snappy feel of 2 strokes. I'm very highly looking at getting an '04 KX 125 or a CR125.
I think they are equal on the terms of maintence, sure you might be able to go longer on the top end but it's gonna be alot more complex to tear apart compared to a 2 stroke. Do yourself a big favor and ride a 250F first before you decide to get one. The 250F is definetly not for everyone it totally isn't the super bike the mags act like it is. I could wax good 250F riders on a 125 all day cause I have alot more confidence in my abilties when i'm on the 125. but totally get the one you feel more comfortable on not cause it's suppose to be the latest greatest 125's are not dead! I feel that 250F's still have a long way to come just my 2 cents.