RTV. Superior to any gasket you can use.
Never use RTV for a transmission pan gasket. Once the excess is squeezed out, it will wind up caught in the filter. Any impurity on the surfaces and that RTV won't stick./quote]
Not if you a) don't over apply and b) let it cure for 24hrs before adding fluid and c) use a wire brush and brake cleaner. It's not like Niagra falls in your transmission or as if you have little gnomes in there hammering away. Once that stuff sets, it ain't going anywhere. And Permatex actually makes an anaerobic gasket maker that comes off relatively easy, where nothing more than a steady hand and a putty knife gets it open. It's specifically designed for use on oil/transaxle pans where servicing is required.
The nice advantage of a set in place gasket maker is it will fill in any undulations or surface imperfections in the pan, something preformed can't do.
Who has 24hrs to leave it? That would really jam up the works if you work on multiple cars a day.
^this.
I always use OEM gasket if available, or Felpro if the OEM price is too high. Both are top notch. Other brands may be fine but rarely much lower price than felpro. I would consider RTV only as a last resort, for the reasons mentioned above.