RTS is my favorite genre, and has been since the mid-90's demo of Command and Conquer and the dozens of titles in this genre that I've played. RTT and TBS have their respective epic titles as well. I'm curious as to what you all are playing out there, what you might suggest, etc.
I prefer futuristic sci-fi and cold war era titles. Here's the list of games I'm currently playing and a few of my thoughts on them:
Planetary Annihilation (Gamma) - Love the scale and options and art style along with performance for number of things happening. Dislike no pause or saving due to server-side hosting thus-far (supposed to change) and no storyline (though Galactic Conquest is promising). I was an original backer for this 3 years ago, and I'm glad to see it coming to fruition and official release soon...this is an amazing RTS imho.
SupCom2 - My 12yo and I play this MP a lot...it features decent scale, upgrade/research, different races etc. Enough depth to get into and have different play styles and also have quicker matches vs. the older SupCom series. Many dog this game, but especially after the last update not too long ago the game has been solid...I've enjoyed it since 2010...yes it shouldn't be called SupCom2 but it's a solid title and very affordable, fun and a great RTS imho. Also check out SupCom2 2013 mod.
SupCom + FA - Excellent overall, except for single core and performance issues. Huge scale, tons of options, but a sloooow pace. For a 7+ yo title, it's a solid title worth owning (get the gold version from Steam). When you want an epic match that takes hours, this is it. Epic. 'nuff said!
Starcraft 2 - A lotta fun, I never got into MP as I'm not an APM player...but it's a lot of fun...one of the best storylines and SP experiences..smaller scale, still a lotta fun. Very well polished, Blizzard proves they still got it for RTS titles...now let's get a Warcraft RTS...I was never a WoW fan...but Warcraft 2 and 3 were epic!
C&C Tiberian Sun - Classic...this title was hugely hyped back in the late 90's...this title got me into online forums, creating websites, I even interviewed the guy that starred as Kane...Joe Kucan I believe. Best of all this classic is totally free! Get it at Commandandconquer.com I just got it working on my Windows 8.1 install on my lappy. I prefer 1280x720 vs forcing full 1080. I wish this title could allow dynamic zoom...beyond that...an epic title from years ago that holds well to the test of time.
C&C 3+Kane's Wrath - Sure EA stole C&C's thunder and hollywood-ized it...but these titles were still badass! Still solid graphics imho, zoom even though limited, but has fast paced action and is still good fun. Kane's Wrath was a very good addition as well. Well worth playing..so is Generals and the Red Alert series, but I won't add those here as these two C&C titles are what I prefer.
World in Conflict - Awesome RTT title, was ahead of it's time in 2007 imho...but SupCom 1 overshadowed it...this title never really came into full force. Still good title. Good stress test too. Good SP..MP is dead though.
Wargame series - Awesome but challenging RTT, steeper learning curve...realistic cold war era units. Better MP..AI is omnipresent which can be frustrating. Up to 10v10 MP. SP is ok...still well worth playing.
Those are the ones I'm playing...here's some other ones I enjoy...
Star Ruler - Indie RTS
Sins of a Solar Empire Series - Epic space RTS
Homeworld 1 & 2 - SUPER EPIC RTS..but very aged. 2 has tons of mods. Both are being remastered for modern systems/OSes.
Sword of the Stars 1 - One of the few TBS that hooked me
Warcraft 3 - Classic RTS...tons of fun.
Starcraft 1- Good and well aged...still fun but SC2 is much more enjoyable IMHO.
I'm sure there's more I'm missing that I'll add. I hope this is the start of a good strategy thread...give your feedback, opinions, suggestions, whatever.
ADDITIONS-
I figured I'd quote and share my C&C Tiberian Sun post from below for new readers. Some good, classic and especially free RTS/RTT options are always handy to have easy access and instructions to. Tiberian Sun is well worth the little bit of effort to make run in Windows 7 and 8.
C&C Tiberian Sun + Firestorm FREE and Working Windows 7/8(.1)