so I've come to the conclusion that I'm going to make a ranger for the RoTRL AP that my group is about to start. I'd love any tips on specifics for rolling this character up.

Right now, my group is:
Cleric: Melee-focused, Half-Orc Shoanti
Wizard: Evocation Specialist, Gnome (pyro blaster)
Summoner: Half-Elf with a Damage/Tank-based Eidolon

I chose Ranger because we need some ranged damage capacity, some scouting and skilled ability, and someone who can hold the line should the Cleric and Eidolon lose ground. On top of that, I hear that Favored Enemy: Giant may be of use here. ;)

I'm working on rolling him up now, and am rolling a couple of things around in my mind:
1. Switch hitter - For versatility in combat (and... Aragorn). Or should I go straight archer? Or straight two-hander?
2. Archetypes: Skirmisher (are these abilities worth giving up your spells?). Any other Archetypes I'm glossing over that are worth a look?
3. Class: Dwarf is a standout vs. Giants, but I want to make sure this character is well rounded above all (the slow speed seems to make for a subpar scout). Humans and Fast Learner stand out as a good option.
4. Anything else I'm forgetting.

Obviously there are plenty of guides out there to optimize the heck out of any class, but many of them sacrifice everything for the sake of martial prowess. I want to make sure my Ranger can be a boon to the group all session, every session.

Whichever choice you go with, I highly reccomend the Infiltrator archetype. We had someomne run a Dwarven Infiltrator and he always seemed to be exactly what we needed whenever we needed it. If I remember correctly, his eventual adaptattions were Fast Speed, Lunge, Resist Energy 10 (Cold, Electricity or Fire), Swim 15’, Climb 15’, Low Light Vision and Iron Will.

He was a Two-weapon Fighter with a Wolf animal companion as well who primarily focused on his hatred of Giants right down to his AP Trait. I actually have that build if you want it - and remember the spell Instant Enemy keeps you very nicely 'well-rounded'...

I have a Dwarven ranger in my group, and he's doing quite well. He's a plain ranger (no archetype) that specializes in crossbows. For melee, he has a shield and Dwarven waraxe. He is just getting to the point where he can take an animal companion.

Your group is relatively similar to ours:

Dwarven Cleric of Abadar (has the travel domain to get a speed boost).
Dwarven Ranger
Elven Summoner (with a dragon-flavored eidolon)
Half-elf sorcerer.

The group has been fairly successful so far. There have been moments when one or another has been knocked out or otherwise incapacitated (as can be expected during the course of normal adventuring), but nothing close to a TPK...yet. MWAHAHAHAHAHAHAHA!

Talk with your GM regarding favored enemies and terrain. It's probably better to let your GM give you that info than get it off the webs (to avoid potentially spoiling info he might want to control.

We also had a dwarven ranger in our group, who used a heavy crossbow. No archetype, crossbow combat style. Once he got to spellcasting levels, he was pretty devastating when he cast gravity bow.

For melee, he picked up an adamantine battleaxe from a side-quest I ran.

I'll agree that you'll want to talk to your GM about terrain and favored enemies.

[I've actually asked my players to stay off this board entirely until we're done with the AP!]

Right now I am running a Ranger in a fresh RotRL campaign and so far I like her alot. If I could, I would suggest looking into the Spell-less Ranger class from Kobold Press. Its a fantastic take on the classic Aragorn/Robin Hood ranger who never had to rely on spells. So if 3rd party material is allowed its definitely worth a looksie, plus the class has an option to forgo ALL favored enemies but 1 (which could be Giant), and allows him to pick up 2 different style feats instead of one allowing you to switchhit even better than Treantmonks because you have more feats to do more things.