Do you really have to ask? Succinctly: SENIORITY-based! It should look like someone on the JNC actually gave a sh'' about the fact that a portion of its membership (including this ired commentator) has been working without seniority for most of a decade now, and that that sort of continued compromise is wholly unacceptable going forward, especially given the fact that time on reserve will constitute at least the first decade of one's "career." I'm on the cusp of completing twelve years now, but I may as well have started yesterday when it comes to trip selection. Actually "trip selection" is mostly a misnomer, because it's de rigeur to be called by daily scheduling to cover the worst assignments that crop up during the day. As a reserve, if your number is up you must do what you're told with absolutely no respect to seniority. In any other work group represented by a union, this sort of thing would be unthinkable to not only the membership, but to, (get this!), union representatives as well!
The tone and phrasing of your question is familiar...evocative of those posed in the recent feel-good, page-turner, "RSV Q&A Pt. 1," and its much-awaited sequel, "RSV Q&A Pt. 2," conceived in the spirit of phony guilelessness and smarmy patronization. If your asking, "...what should the ideal reserve section look like?", is designed to render me unable to provide the detailed minutiae vis. the logistics of an "ideal" reserve system, you have succeeded. I don't know, and therein lies the necessity for negotiators with no other agenda than aggressive advocation on behalf of the membership. And that means seniority counts for everyone. No exceptions. Securing a seniority-based reserve system will become even more imperative as new-hires will be on the property in coming months. Imagine the resentment of those of us who have been around, or furloughed, or displaced, or quick-called ad infinitum for years on end, being told, as the TA permits, that the grouping is closed, you'll be working the sixteen-leg four-day, and the eleven-years-your-junior rookie will take the three-day Rome trip.