I was thinking about buying a preowned Jeep or toyota. i ws wondering which would be the most reliable. i was tyhinking a '90s jeep yj with the straight 6. but i really have no clue.  

Let's cut to the chase. If you are looking to buy a YJ, for whatever reason, buy a '91-'95 with a manual transmission and the inline-six. Im not saying all other YJs are junk, Im just telling you to save yourself a lot of trouble in the long run and get the good stuff up front-a multiport, fuel-injected 4.0L engine coupled to an AX-15 with an NP231, better heater, and it's less likely to be hacked up or rusted out. All of these components make for a nicer Jeep.  

I'd go toyota. i see hours and hours of dangerous colorado wheelin' in arguably the most unforgiving circumstances in the continental states, and ive seen my share of mishaps on the trail. i've wheeled XJ's YJ's CJ's, but i can assure you that in stock form, a toyota landcruiser is beefier than, and will take more abuse than an unadulterated jeep. That's all opinion though, so if you don't want to replace your rear main seal every year or worry about those flimsy dana 30s out on the trail, buy a toyota. (oh yeah, toys don't have that unibody *** either, so they're more sturdy and better to build.)
the aftermarket is huge for toyotas and is competitive worldwide, which brings quality at decent prices.
I personally prefer the 'cruisers. Straight axles front and rear, gutsy straight 6 engine and plenty of aftermarket, you can't fail. i've heard toyota engines are rated at 400,000 miles and with 250,000 on mine and considering how it still starts with the first turn of the key, and burns clean, i can believe it.  

It probably boils down to your budget. I gotta agree, it's tough to beat a solid-axle LC, but they're not quite as plentiful on the used-vehicle market as YJs are, and a 40- through 60-series Cruiser in good running order with a straight frame and body panels can cost you upwards of $10 grand (at least where we live on the Left Coast). A fair-running high-mileage YJ can be had for a lot less in most places.

Regardless, though, if you opt for the Jeep, go for the '91-and-later versions as the Peugeot five-speeds that came in the earlier models were junk. If you go with bigger tires down the road, be forewarned, the Dana 35C rear axle becomes a weak link pretty quick.

Another budget solution I'd recommend is an '84-88 Toyota 4Runner or pickup. True, you can only get 'em with a four-cylinder motor, but those little trucks have a well deserved reputation for being pretty much bombproof. The engines were typically good for up to 250,000 miles, and the stock axles can handle tires up to 35s without much problem, though you'd wanna swap out the front Birfield joints (in the '84 and '85 trucks) for some stronger pieces such as Marfields or Bobby Long joints if you do any kind of extreme wheeling. Just my $.02.  

I think what we all really need to know is what your budget is...  

agreed, the budget is the real question here. Additionally, i also agree that an older toyota pickup or 4runner will do the trick, but it's not necessarily down to just 84-88's. depending on your level of mechanical aptitude any toyota 4x can become a real solid wheeler[i'm not counting highlanders in that assessment], and if you're not looking to build an aggressive trail rig you might find that a 95 or higher 'runner has better highway manners, a good amount of power and, (at least in my experience) you'll probably pull down better MPGs than a jeep. Yes, jeep fanatics will tell you that the 4 litre would rip a toyota 3.4 an new one, but guess what else it'll rip a new one: the cheap powertrain! Daimler chrysler is going under, and has been for some time, and what do struggling auto makers do? take shortcuts, that's a lesson in basic detroit economics. what good is all that torque if all it's doing is breaking components.
Another applicable question is what the hell do you want to do with it? if you want to go get groceries with it, a jeep might be reliable enough, but if you want to hit mineral creek road in a downpour, get a toyota.