electrical system upgrade

When looking at alty's do I need to look at max amps or at amps at idle. Ebayed some I wire gm's. One was max 220 at 1200rpm but 105 at idle for $170 then they had one that was 300amp and 150 at idle but it was $395

i would go by idle. i think amperage at idle is more important that max amperage. but 220 at 1200 rpm isnt that bad that isnt that high of an rpm. and 105 at idle would be a huge step up from stock 55 amps tht the mazdas have. lol. should be enough to recharge a good battery and keep up with demand on a small system and compressors