If your finances can handle it, #1 is going to be the easiest option. You'll be able to choose the plane
you want and set the terms of the partnership agreement. As
@NealRomeoGolf has done in post #2, you can even make them non-equity partners or sell less than half the plane leaving you the majority owner, priority and ultimate decision maker (i.e. you decide you want to upgrade to glass and your partner doesnt want the expense, you can still decide to move forward with it by issuing more "shares," buying those shares out of your pocket and diluting their ownership). Option #1 is riskier if you cant handle the finances of owning the plane as the partner(s) can walk away and enforcing the legal agreement takes time and money that may not be worth it in the end. Finding your first partner or a replacement partner may also take some time so you'll need to support the plane yourself.
Option #3 is going to be the second easiest option and easiest option if your finances wont support the plane ownership outright. It's a bit of a trade-off, do to the limited partnerships out there, you're not going to get the plane you want but since you dont have to buy into the partnership, you're not going to end up in something your unhappy with either. You'll also have less authority over the plane and decisions made.
Option #2 is going to be the most difficult option. You need to first form the partnership and agree on a price then you have competing interests/missions in choosing the plane and equipment it has and even if you agree on the type of plane, you can get arguments over things like appearance (worn paint or ugly scheme, ugly but good condition interiors, etc) or stupid things like the N-number. Once you have the plane, the option runs just like any existing partnership but as where options #1 and #3 might have arguments down the road about upgrades, option #2 is opening up the door right out the gate for arguments between the partners. Its also the option that is most likely to end up with a plane that you are least happy with.
Partnerships are difficult but they can be valuable. The non-equity partner idea is a good idea but you'll have to be choosy with your partner in that situation. Without any skin in the game, the "partner" can treat the plane like a rental and beat the crap out of it with very little liability.
Considering you're looking at possibly an arrow, I would suggest you really look at how many hours you're going to put on the plane each year (60-100 hours is a big range and a big difference) and possibly look into PlusOne Flyers or Pacific Cost Flyers. Both are flight clubs in the San Diego area and you may find that at the 60 hours a year, your fixed cost of owning the plane even split 50/50 are going to be more than renting.
Quick Math:
Running Costs:
$20/hr Engine Time
$50/hr Fuel & Oil
$70/hr
Plane (60,000) + Interest = $600
Tie Down Fees = $500
Annual = $1200
Repairs = $1000
Insurance = $1500
Total per year = 4800
Total per partner = 2400 in fixed costs
This is just a rough estimate with only a small budget for any additional maintenance costs but if you do 100 hours, then your total operating costs are going to be $94 per hour. If you do 60 hours then your total operating costs are going to be $110 per hour. At some point you start getting awfully close to the rates the clubs charge and the clubs not only have 100 hours inspections and are a no-fuss operation (you dont have to worry about care or maintenance) but they also have other planes available should your mission/needs change for a given flight.
I'd have a real hard time competing with them if I was in San Diego.