Although I already have a post in this thread detailing my thoughts on Pinsir, I'd like to respond to some of the comments I've seen about it.
I'll start with what's obvious: typing. Yes, Bug type attacks are not going to carry anyone all the way through this game - so it is fortunate that Pinsir has access to a fair vairety of Fighting-type moves, and it can also learn Rock Slide and Bulldoze, both of which can offer great coverage alongside X-Scissor and Brick Break / Superpower. As CJorex said, it isn't much of a wait for Pinsir to learn X-Scissor at Lv. 29. One of the reasons for this is that has Brick Break when you catch it, a move that makes dogmeat out of normal-, dark- and steel- types. If you caught it after Elesa (like I did) it can still be ready for Clay's Gym by the time you get there. In addition, X-Scissor is a reliable STAB move, and once you have Swords Dance you more or less have a bread and butter sweeper that can handle most trainers and grunts.
I often used Pinsir as a lead and I was quite pleased with its performance - most of the time I only had to switch out if the opponent could directly threaten it. It has a field day against Zinzolin's mons, and Colress's too; and it did great in the Plasma Frigate, and other opporunities to abuse Rock Slide in double battles. I've been into details about its performance in important battles in my earlier post, but to summarise, it is useful in gyms not including Skyla, it is great against Caitlin and Grimsley and fares well against Iris if you play it right.
I actually decided to just suck it up and try it out in the Elite Four. I didn't have much trouble with them (beat the Four themselves first try, and Iris the second), but it was because of the rest of my team, not Pinsir. It did do pretty well against Grimsley, but I couldn't keep it alive against Caitlin (switched it out of Sigilyph for obvious reasons, and couldn't switch it back in), it's complete junk against Shauntal, and I didn't try it against Marshal because I used the strategy of setting my Claydol up with X items instead. I couldn't make it work against Iris either; anything I wanted to hit with it could outspeed and OHKO it. Perhaps I was underleveled, but I couldn't really get opportunities to set up Swords Dance even against random trainers; it was mostly a dead move. (Although, of course, one way to measure "how good is this Pokémon ingame" is "how underleveled can you be while still performing well with this Pokémon"?) If you want an idea of my levelling rate, I was at 57-58 at the Elite Four.
All of this in mind, to make the best use out of Pinsir I recommend you run Swords Dance with X-Scissor, Rock Slide, and either Brick Break or Superpower. If you're worried about not having a chance to set up, 85 Spe is still good even when you have a Sassy nature (like mine did) and 60 HP / 100 Def / 70 Spd is not too shabby either.
I didn't think of Rock Slide (and possibly don't own the TM); I was running X-Scissor / Superpower / Swords Dance / Strength. The problem was in defences, more than in any of the other stats; it couldn't take more than one neutral hit, and opponents could often hit it supereffectively. (Because it probably matters, I was running in Challenge Mode, Set-style battles for difficulty purposes. Switch versus Set should probably be explored more in the tiering, because some moves, like Charm, are much better under Set.)
It's also worth noting that Pinsir is not commonly found in Lostlorn Forest: what is it, 5% encounter rate? 10%? I was fortunate to find one in under five minutes, but I suspect if I had looked for a different one I would have been shuffling grass for a while longer.
It's 20% according to the source I looked at (albeit not a 100% reliable one).
And looking through the thread, seems that there aren't any suggestions about Baltoy > Claydol, so because I was using it:
Name: Baltoy - Mid Tier
Availability: It appears in Volcarona's room in Relic Castle, which is accessible after the PWT, but it requires a very large detour from the normal route through the game. Actually getting it to appear isn't hard once you've done that, but you still have to have beaten five gyms, so it's a way through the game.
Stats: Baltoy's stats are pretty good, but Claydol is fast enough for in-game, has plenty of SpAtk, and is bulky enough that it won't usually die in one hit even to a super-effective move.
Typing: Ground/Psychic with Levitate gives a very valuable set of resistances to Ground, Rock, and Fighting, which is frequently used as a STAB+coverage combination by in-game trainers, and being immune to Electric is nice. It also has several weaknesses, that need to be covered by other members of your team. The STAB combo hits most of the enemies you'd want to use Claydol against super-effectively, apart from the occasional Flying-type or Levitator.
Movepool: The main STAB you'll be using is Extrasensory/Earth Power. Extrasensory is obtained almost immediately, and the move you'll be relying on to start with. Earth Power comes later than you really want it to at level 40, but still early enough for you to get a lot of use out of it. The level-up movepool is quite shallow apart from that (although there are options like AncientPower and Cosmic Power), and there are some interesting TM options like Ice Beam and Shadow Ball. For "HM"s, you have just Strength (which is mostly a waste of a moveslot) and Flash (which is a waste of a moveslot, but which can be deleted because it's technically a TM, and so can just be repeatedly swapped with another TM move).
Major Battles: Most of the Gym Leaders you'd want to use Claydol against have sadly already been beaten by the time you get it. It does pretty well against Colress, though, and later Marshall (I soloed Marshall with mine, although this requires a bunch of X items for setting up). Its strength is more in beating the more ordinary sort of trainer.
Additional Comments: When you get Baltoy, it isn't very good, but it gets better and better as the game goes on; its unusual typing, with the option of a couple of good coverage moves, is pretty good at shoring up weaknesses a team might have to Electric and Fighting in particular, while not being useless against other types. It's also OK for use as a pivot, or something to send out while you revive other members of your team, and works well with strategies like X item stall. By the end of the game, it's doing more work for a team than such in-game powerhouses as Azumarill and Magnezone; it just takes much more work to get it there.