I have an old , like 1990 specialized rockhopper
Recently I’ve been putting together a Cannondale 29er from the frame up
A lot has changed in looks like in those 30 years.  I mostly just rode rails to trails and used the bike to get to fishing spots off some trails.  And this will continue to be my preferred style of riding.   No flying down hillsides at the local ski resorts.  

where my old bike had three chain rings up front and then 7 on the back wheel cassette,  I now see photos of al these new bikes with only one chain ring up front and cassettes up to 12 rings.  
So apparently that is now the preferred way to go?   Or it that something for mostly the downhill riders?  
RTR is not exactly rough pedaling, although there are some local trail with some amazingly pretty steep grades and some not too punishing side trails that spur off them.  No issues with the new setup pedaling up steeper grades or hills?

So for my style of riding should I go with this New setup, or looks for some older cranksets with three chainrings and then just a seven ring rear cassette?

You need that tiny front ring if you are doing steep climbs.

Some of them are just easier to walk up.

I love 1X gearing. It blends well with having a dropper post. My fat bike has traditional gearing with a front derailleur, my MTB has 1X. When I riding my MTB I have never missed having a front derailleur but when riding the fattie I have wished that I didn't have to shift the front chainring.

1x11 or 1x12 is the only way to go. Everything else is obsolete.

1x for sure.  1x11 on my Norco, wife has 1x9 Microshift and loves it.

I would be looking at Box Prime 9 if I were building, unless you really like sitting at one specific cadence and load.

My riding is similarly limited in regards to terrain.

I switched from a 3 x 9 to a 1 x 9 and I can't see ever going back to multiple rings.  Heck, I'd probably go Rohloff (13 speed internal gearing rear hub....very expensive) before I'd go back to multiple chainrings.  

Thanks for all the good replies
Obviously I had no idea how much things have changed.  

I am going to look deeper into the new rear shifting systems nice article here in Singletracks

I think that is cool stuff.

I still have 3x11 XT on my XC bike. I'm old and need as much help as I can get. I also ride on the road a lot so....
1x is handy and slightly lighter overall but you do give up some gearing. If you're strictly riding trails and aren't worried about long gradual inclines, 1x is handy. If you're going to ride on roads also, especially roads with steep inclines, 33 speed has it's benefits, IMO. The ability to ride up a 1/2 mile incline when 1x guys are walking their bikes is a nice feeling.

Going to a 1x11 will give you a very broad gearing range, while still maintaining reasonable sized jumps between gears.

Also, going from a 3 x 9 to a 1 x 9 (eliminating 2 chainrings, a shifter, a front derailleur and cabling) took a full pound off the weight of my bike.

That's a load of bs.

Especially with the smaller size of most single chainring setups. For primarily rail trails, a multi ring setup gives you a ton of flexibility. You have road bike tall gearing, and ultra low also if ever necessary. I need at least a 48t ring for mostly level cruising, but when things get steep can drop that down and have not just more, but more appropriate gearing with the smaller rings. I even just built a Trek 920 frameset as a 3x8 for my crushed stone rail trail riding, and it is perfect for that. And it will still go ultra low if I ever want to do more mtb type of rides. Just because it's no long the new hotness doesn't in any way make it obsolete. In fact, to me it's a necessity that I can't find on any 1x system.

It isn't bs.  Out of curiosity, how fast are you moving on that 48t gear?  20 mph?

To each his own. Nothing wrong with 3x7, 3x8, tubes, cantilever brakes, no suspension, steel, 26ers etc. There’s always the latest trends, especially if you’re a competitor or into extreme high flying riding. If you think you might do touring, bike camping, just general off-road touring, trail riding, climbing, I would go with the traditional/old school tech. Easier to work on.

You need a 48x11 to cruise? That is 33mph on a trek 920.

1x solutions don't *quite* offer as much gearing coverage as the 3x7 config did.... but that's OK.  Unless you're talking about the very WIDEST range 1x setups, they don't quite have the coverage of 2x setups... but again, that's generally OK.  Why?  Because it's pretty rare for you to be flying along at 30mph on an MTB and still pedaling trying to gain more speed.  If the downhill is steep enough that you'll spin out on a 1x, it's steep enough you don't need to keep pedaling.  

As to the steep hills, set up your chain ring and cassette so that you have 18 gear-inches (tire diameter * (chain ring/cog)).  That's really about the lowest gearing that still makes any sense, and you should be able to climb just about anything you can get traction on.  So, for a 29er, say a 28 tooth chain ring with an 11-46 cassette.  In your small chain ring with a cadence of 100rpm, that puts you at about 20mph, which for a lot of people, is plenty fast for pedaling (not coasting downhill).  The time that breaks down is if you're doing XC racing or generally riding on relatively flat, smooth trails.

That gives you a basic place to start.  If you're spending more money, you can go wider range and get more gears.  If you're a stronger rider, instead of sizing your chain ring for 18 gear-inches, go up 2 or 4 teeth.  If there is a downside to a 1x setup, IMHO it's this:   There's often a BIG gap in gearing between 1st, 2nd, and 3rd gears.  If you spend a lot of time slogging up steep climbs, sometimes you wish you had a little more "in between" gears in that range.  If your trails are more up-and-down, or they aren't steep, brutal, long climbs, that's not as much of an issue.