What I'm talking about is the skill trees, currently I'm playing a powertech but this applies to all other classes as well. Is it best to concentrate on a single skill tree and reach the highest tier, or spread between two (maybe more weighted on one), or too spread myself across three? And should the same rules apply for all classes?

I'd appreciate any advice

Depends on the AC and your goals. I don't know enough about Powertechs to comment intelligently about your available build options, but there are some hybrids that are as good or better than their single-tree peers, and there are some hybrids that are flat-out inferior.

Your best bet is to head to your AC's (and the cross-faction mirror's) subforum(s) and read up.

EDIT: If you're leveling up, it might be best to spread your points around liberally at first to pick up low-end talents that help in the short term, and then respec at level 20-25 with a more solid plan. I think that's the only strategy that can be safely applied to all classes.

In general, it is best to specialize in one tree.

There are only a few hybrid specs in the game that work across all the classes at endgame. And those are hybrid only in that they don't pick up the (2) highest tier talents.

Also, there are a few times while leveling it is best to beeline to X talent in one spec then move over and focus on another spec, or respec later. These often aren't really true hybrid builds but can make leveling easier.

Powertech dps can do very well going most of the way up pyro, then taking the +9% aim from the tank tree and improved cylinders from the AP tree. Otherwise, stick with one up to the top before going to another.

This is for PvE, btw, I know next to nothing of PvP builds.

What I'm talking about is the skill trees, currently I'm playing a powertech but this applies to all other classes as well. Is it best to concentrate on a single skill tree and reach the highest tier, or spread between two (maybe more weighted on one), or too spread myself across three? And should the same rules apply for all classes?

 

I'd appreciate any advice

Personally, I have never met a hybrid class I like on any MMO and some (like WoW) have made it so they're impossible to make. I like to concentrate on single-trees because they're much simpler to manage and I don't have to invest time and effort into making and testing a custom spec that turns out to suck anyway.

In the case of the Powertech, I play one for my main class and I assure you, whatever tree you pick if you completely level it to the top ability and branch out afterward, you will not be disappointed. Shield Tech and AP are great for PvE, and Pyrotech rolls so much face in PvP there are entire threads on the PvP forums made by people who want to see the class nerfed into oblivion. It is hands-down my favorite class and I eagerly await a dual-talent patch so I can get both my PvE and PvP fun at the same time.