There are tons of these threads, so you may want to read others to see people's opinions. At the end of the day what matters most is that you get what you want and you get what works for you. But a few things to consider:
Layout:
60% - Bad for gaming IMO. I still do it because I love the aesthetics of a 60% board, but this thing is really missing a few important things for gaming (ex: standalone F-Row). Boards to look for: Poker X, Poker II, Pure, Korean Custom
Mini/75/84 (many names, not sure correct one) - My personal favorite for gaming. Example:
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(https://i.imgur.com/7O069tb.jpg)
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People complain that the layout takes some getting used to (it does, but is totally worth it IMO), and the keycaps are annoying to replace on these boards. Boards to look for: Noppoo Choc Mini, Keycool 84, KBT Race (and Race 2).
TKL - I respect this layout as the best all purpose layout for the average users. However, I'd prefer 60% and mini layouts. Again, PERSONAL PREFERENCE. Some people here hate 60, hate compact, and love TKL. YMMV
Full Size - Disadvantage is that the board is oversized and forces your mouse hand farther away from your QWER/WASD/1234 hand (commonly called the left hand). Most games do not require a numpad, and numpads can be bought separately.
Switch Stem:
Linear: Red/Black - Perfect for FPS. The keys actuate about half way down the press, so you can "hover" the sweet spot for easy multi tapping and awesome WASD control. I do not like it for RTS as much unless I've practiced with linear for maybe a week to get used to it again. Then linear is my favorite for RTS also.
Tactile (Low): Brown - Not very tactile IMO. I much prefer clears. However, browns start their tactile point a little bit down the key press, rather than at the top like clears
Tactile (High): Clear - Much more tactile than browns. The bump is so much bigger that with light springs the key gets stuck on the upstroke.
Clicky: Blue/Green - Bad for gaming. Anyone who says otherwise has not looked at how the switch is designed. Don't get me wrong, you can still game in blues. However, in order to get accurate clicky feedback, you need to release the key all the way to reset the click mechanism. Hovering is still possible, but you do not get the click if you hover and fail to fully release the key. Some people game better in blues. I will say that is very true, you can game on blues. But do not try to argue that they are poorly engineered for gaming. It's like saying you can run in basketball shoes, some people prefer running in basketball shoes, but they are poorly designed for running (heavy, much ankle support, etc etc etc).
Clicky (Soft): White: I'm still looking into it (you can find other people's answers on this forum), but I cannot explain why white switches are a softer click than blues.
Springs:
Red/blue/brown all share the same light-actuation spring
Back/green/white all share the same heavier spring
Clears have a very unique spring which is lighter than black spring for the first half of the press, but becomes much heavier the farther down you go in the press. Hard to explain.
Low quality photo of common cherry switches:
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(https://i.imgur.com/4kJPyAV.jpg)
Topre is a whole nother topic. People say Topre isn't great for gaming, but honestly I've gamed on all switches and gaming on any switch is doable. Personally I do not recommend Topre until you have tried many MX. Topre is a great switch, I love it, but I would not recommend it as a first or as an only keyboard.
Try them all, collect them all, love them all. Hope this helps, sorry if spam.