I'm thinking of picking one of these up, excluding 1+2, which would people suggest getting?

Yess! Thank you GOG!
You can't go wrong with any of the latter three, although I'd recommend starting with Under a Killing Moon. If it strikes a chord with you, buy the rest. If it doesn't, well, you're short a measly five bucks. =)

I would suggest 'Under a Killing Moon' or 'The Pandora Directive' if anyone has yet to grab them. Personally: I liked Pandora slightly more than UaKM, and have yet to properly get into Overseer.

I agree with Ois. The Pandora Directive is longer, slightly better and much less corny than Under a Killing Moon, but you might miss some references to UaKM if you start with TPD. UaKM gives you a great introduction to the character Tex Murphy and to the atmosphere of mystery these two games convey.
Overseer is slightly different from UaKM and TPD in terms of presentation, which I didn't consider an improvement. Overall, I thought it was a lesser game in comparison.

I bought them all when they were 30% off one weekend and definitely would recommend people buy them at 50% off

Overseer hasn't aged as well, no. It was trying to be fully 3D and photorealistic long before such things were remotely viable. Plus the massive instability of the Cell Block area killed the game for me. When you can't even complete a game because of bugs, it's difficult to recommend.

Hell yeah!!
I remember playing The Pandora Directive right after the premiere some 13 years ago. It was just a fantastic experience :) It was also one of the games here on GOG I bought right after it was available.
After Christmas promo I got Mean Streets and Martian Memorandum so there were only 2 more Tex Murphy games I never played.
$$ And now my collection is complete :) I'm so curious about UaKM. I've heard the plot is really good :)
Thanks GOG :)

Sadly, I also bought Tex Murphy 3+4+5 (30% off) before this promo, maybe there will be a chance for alternative offer?

Just buyed Overseer, now my Tex Murphy collection is complete. :)

No, that was only when they gave TM 1+2 away.

Ah, I own them already so my purse can rest for a moment longer.

Nice, all i was missing was The Pandora Directive, and now i have them all!Yeah i would suggest playing the last three games in order, and definitely all of the last three as they're all pretty fantastic.
I actually played Overseer first, which was fine since it's a retelling of Mean Streets anyhow, and i found it to be great.I did play the DVD version so having a relatively superb video quality and no disc swapping probably helped the overall experience with it, and i found a bunch of save games to help me get past any problems there would be with any crashing points, of which there were a few.

They are all classics and all worth owning. Especially for these prices.

I picked up Overseer, the only one I didn't already have. Having finished Mean Streets in December I think it should be fun to play through a modern version, without the pointless "flight simulation" and other eccentricities of the original game. For five bucks it's hard to go wrong.