I wouldn't recommend a Montreal for your first Alfa experience. The reasons are really too many to even begin to explain on a forum like this.
Your idea of looking for a GTV, is a much better way to start your journey into the arcane mysteries of Alfa ownership. I have a '71 1750 that I love. They can be very good cars.
Best of luck on your search!
It's not really a matter of reliability. The issue is, a Montreal is far more complex than a GTV. Parts are unique and hard to get, and much more expensive when you do find them. With any special car like that you will join a very select group of people who spend lots of their spare time hunting for parts and trading information on arcane things like how to tune up the special SPICA fuel injection pump that's only on Montreals. For some people that's a lot of fun but it's not for beginners.
A GTV is an excellent starting place. Simple to work on, most parts readily available, and a GTV is really one of the best all-around sports cars ever built--excellent handling, good power, good looking.
thefilmmaker had asked: "do you mean a GTV is generally more reliable than a Montreal?"
Not that Montreal's are unreliable, but yea, a GTV would be a better entre into Alfas.
Parts for a GTV are much easier to find, and much less expensive than Montreal stuff. Many GTV's and Spiders (they're identical mechanically) were built, so used parts and expertise are readily available. Montreals were built in very small numbers and never officially imported to the States - trim parts are very scarce and mechanical parts are costly.
You mentioned that this would be your first Alfa - have you owned other collector cars? If you have a fleet of OSCAs and Lancias, maybe a Montreal will seem mainstream. But if a new Mini was your prior choice for an offbeat car, then you're in for some shocks as a new Montreal owner.
The Montreal was never imported directly into the US market, so all cars here are so-called gray market cars. Parts and service are far harder to get, and the car has several known issues regarding engine reliability (very expensive to repair), and are prone to rust. GTVs also tend to rust, but there are so many more of them you can still find a good one if you look. Montreals are much rarer, so the choices are few. Most Alfa specialists have seen so few, and so rarely, they don't really know the car well. Parts will be a constant search even for the commonplace. If you don't have a support network already established, the car will probably be inoperative for long periods for what should be small problems.
I have never owned one, but my opinion is based on hearing horror stories from several former owners, and knowledgeable technicians.
In any case, if you get serious about the Montreal, be sure to have it thoroughly checked-out by a competent Alfa specialist. That alone will alert you to how little support there is available for these cars, and may help you avoid the financial suicide of buying a bad one.