Well will throw in my two pence worth! If you are training on the C-172 then I would stay on this plane. The complex time is not really what you are after anyways. That would be the multi-time.
The reason to stay on the C-172 is that all though the complex single is not that complex, it is another thing to learn and whilst you maybe a great pilot, it is hard enough to master all the skills of IFR in the time that you have without worrying about the complex stuff.
Speaking as an instructor, only an FAA one, but none the less an instructor. I have seen my students struggle with that extra lever and how to use it, it just makes them uncomfortable. And is like the preverbially straw and camels back.
I used to introduce the complex during the long IFR cross country when we had time to go over some of the systems, obviously with me showing the student how to do most of it and what to set for power. The other reason we used it was that it had nice avionics. ( Dual Garmin 430s)
I guess that you will be moving onto commercial after Instrument and you will do your complex hours then anyways so just wait till then.
As for picking up the other planes at the new school, they will most likely want you to fly a couple hours with them so just use those hours to get used to the new planes and kill 2 birds with one stone.
Well hope that helped.