The OP has already stated he is going to do the right thing and replace with full frame windows and not inserts, as I also suggested up thread.
James4B, no reputable window dealer is going to offer/sell windows without LowE coating and without argon or equivalent gas for home replacement windows, and it is code in most all jurisdictions for new construction (possibly even for replacements in some places). The added cost ~10% will likely be recouped in several years of heating/cooling seasons and the home will be more comfortable. For resale a future buyer will expect this from replacement windows.
Good manufacturers will have their windows tested and certified with ratings for overall energy efficiency, water & air infiltration, strength. Look for energy ratings in the low to mid 30's. This is a place to start to learn some more.
http://www.nrcan.gc.ca/energy/products/categories/fenestration/13939
Triple glazing (~+20% cost) might be appropriate if noise is an issue or located in a colder region of country and on windows particularly oriented to the north & east, or someone simply wants better and is less concerned with return on value. Rough R values for windows are R2 double glaze(no LEA), R4 double with LEA, R5-6 triple with LEA. So compared to the wall insulation values ranging R12-R30 depending on age/construction method windows are a huge weak point, so gains are harder come by. New inert gases are being offered more recently so there may be some options there I'm not current with. Biggest factor is properly installing and sealing them well.
Window type is also a factor and casements will always perform better in wind, water infiltration and energy tests, but the difference is not huge. Single hung verticals next followed by horizontal sliders.
A good window vs a bad one- many things- quality and sealing of vinyl extrusions, is frame incorporated (1 piece) or pressed/pounded on (2 pc) quality, number and type of materials of closers, locks, cranks, screws arms, spacer type between glass, quality & number of gaskets or seals/fins, amount of fill % of inert gas between glazings, ease of use, warranty and fine print to name some.
To the OP if your windows are small in the bedroom you may have to consider the available opening area of the window if they do not meet your current building egress codes, although if they don't now identical replacements may be allowable, but necessarily safe.
FYI, I worked in the industry retailing and offering installing services for years in my phase down career before retiring, representing a leading manufacturer in this region.