I'm a roadie, have a buddy into mountain biking, he keeps sending me gopro vids of his rides and it looks pretty cool, I'm looking at 2 cannondale f900s, both 10 yrs old and in great shape, little use, one is 300, the other is a lefty for 350, pretty sure they are both either 1999/2000 models.

Which one would be a better choice? I would say both are in very good/exc condition
The lefty looks cool..

Would say neither unless they are very very cheap.

Fogetting that they may be in in great shape for their age, the geometry on mountain bikes has changed, a 2012 bike will ride alot better than a 2000 model, riding has changed, what wasn't riden 10 years ago is now, and most things a lot faster.

On both you will need to check the rear disc mount, if not IS or Post, you will have issues with getting spares / replacement.

For the headshox model this may have issues with the disc mount size is non IS (international Standard), and you will have issues if you need a shorter stem, as they use a non-standard size.

For the Lefty, yes they look different, but you can run into issues with the specs on them not relating to anything modern on the early models (this is on of the early ones). Getting spares maybe an issue, but the disc mount is most likly a non-current standard, with non-standard mount, bolt pattern size and rotor (there was a post on this recently), which will mean when it brakes / wears out / needs service, it's junk.

You can see the orginal specs here https://www.bikepedia.com/Search.aspx?Q=cannondale+f900, looking at them, they were poorly spec'd for the orginal asking price, a lot of the money would have gone into the front shox on both frames.

Thank you for the time to explain that.
I'm going to pass on both and look for something
A bit more current.

Not sure what your price range is, but both Specialized and Giant make great entry level hard tails around the $800 mark new. 29ers included...

May be worth saving a little longer and getting something modern that doesn't break the bank.

Yeah, I think MTB technology has progressed way too much in the past 10 years to even consider those bikes, heck even in the past 5 years. If I were buying used, I'd try to stay with something that's at most 4 years old for a frame and definitely newer if for a full bike.

Thanks... Funny because that's exactly how I feel about road bikes, and did not really even think about mtn the same way.

In fact if you have any old bikes at all, like older than five years, you should probably gather them up and send them to me because you don't want those old bikes just sitting around your area messing with your mojo. Start fresh with new, modern bikes, but first give the old fashioned bikes to me.

I have had both bikes in questions the disc brakes only issues is that my guess they are four bolt rotors not a huge deal just replacements are hard to find(hope). Stems again same thing odd not impossible. Bigger issues would be rebuilding either fork. The caads3/4/5 frames are darn good and have taken anything i threw at them. lx and xt drivetrain works fine the orginal brakes on both stink. I would pick the best condition one if you have to, or buy both sell one to me. pics of bikes in question could help tell years https://www.vintagecannondale.com/

I like the Cannondale headshock bikes. I'd consider either of those bikes, if they were priced correctly, say around $200.

I ended up with a 2000 f900s headshock for 250$, it was well maintained, recenty tuned, headshock rebuilt disc pads etc... Figured for the $$ it's a good way to see how much I like mtn biking

Good thing you didn't get the one with the lefty, while the lefty is a good fork, it didn't come specced on a 1999 or 2000 F900, the lefty didn't appear on cannondales until 2000. The lowest offering with the hardtails that had the lefty was the F2000SX in 2000 and the SuperV 700SX for the full suspension bikes.

I guess I could be persuaded to take a couple of those old POS things off of someone's hands too. You know, so that they don't have to deal with such out of date nonsense. I would even go as far as recommending that people should probably get a new bike every year to keep up to date. I'd even be nice enough to pay shipping to my place so that I may dispose of their garbage from last year for them.

I had no idea that trails had become practically unrideable on my 2005 Kona. Thanks for letting me know!

If you equip the 05 with some nice wooden platforms, you will be given trail access.

The lefty was probally the f2000sx.. He was the origional owner and bottom line was 350$, I may have gone with that one but the other was 100$ less and only a 25 min ride away, the lefty was about 90 mins away