I think most ranger may agree that the summons we have access to are not worth the SP at times, at higher levels to get access to summons that are generally weaker than most things you will encounter at level. I think the time has come to change them, or get rid of them and implement a new summon system. So either increase the strength and level of animals summoned or try this.
Familiars.
How Familiars would work would you can summon from a list a group of familiar animals that boost certain skills or have certain buffs. For instance.
Falcon: Perhaps +5 to spot, maybe increased bow speed.
Cat: Perhaps a small boost to dex, or maybe a dodge bonus to AC
Rat: Maybe boost melee attack speed or give +1 or +2 to dmg/att
Bat: Perhaps a small HP Bonus. At later levels perhaps it could even give a lesser vampirism effect to weapons.
Familiar Animals cannot directly attack so have 0 chance of dying or even being hit. Unless their masters die of course. You could perhaps use the models for bats already for falcon and of course bat. And perhaps a shrunken version of lion for cat, and rat obviously = rat.
All these could be given tiers and replace the current summon system as summon familiar spells. or perhaps could be enhancements. I just find it sad that most summons are miles ahead of our small array of choice. If implemented these would have to be available to all Rangers, no certain prestige class I think should have access to specific ones and not the others. Even if certain ones do benefit them greatly. This is just an idea, I hope someone takes the time to read this and at least admit the Ranger summons are lacking a much needed boost in power.