Indeed there are cases in which one can use the M (Manual) mode. But usually these cases are rather corner cases, especially for us, the beginners. Basically you ditch the DSLR's photometric engine which does most of the time a very good job, (except some rare situations in which the illumination is very tricky, you want to achieve very special effects etc.).
Besides that, it is enough more difficult to play with four variables (Aperture, ISO, Speed AND the exposure indicator (usually a vertical beam in viewfinder)) compared with two variables (ISO & Aperture or ISO & Time respectively) or with just one (Aperture or Time - if you have the ISO set to Auto).
The main difficulty here isn't that someone (you) can cope (or not) with four variables in a simulator but to adjust them quickly and exactly in the field given the very short amount of time which you (the photographer) have at your disposition to take "the shoot".
That's why the most photojurnalists (from which, more or less, is your truly also) avoid the M mode. OTOH, I have very close "brothers" which are 'studio creatures' which prefer the M mode.
And now to respond directly to your question, having the Tv (or Av mode) will give you a much 'closer to real' simulation (especially if you are on-field, on-street, on-sports etc. photographer) and will allow you to concentrate rather on the effect you want to achieve (for ex. how to simulate a good moving effect of the child's rotating toy) in the smallest amount of time (think that in the real world, the children aren't so frozen like the one in our simulator :-) ) and not to concentrate so much in obtaining a correct exposure. Usually the metering system does the job rather well. These systems have enough advanced features today to help you in avoiding the M mode with its quirks: exposure modes, over/underexposing by 1/2, 1/3 EV etc.
HTH
PS: Disclaimer: No, I'm not against the M mode. But I want to stress its limited usage today. Of course IMHO.