VC's love to see a solid team and a solid background in the team. The team needs to have some kind of past preferably. Vc's want to see that your team will be able to survive the hard times in building a business. Having been through techstars and interviewed with YC i know the things these guys are looking for and its key you have prepared answers to them if they ask.
Get a partner you can trust and have done something with in the past
Preferably one you have had past dealings with. Any Investor wants to see you guys stick it out even when the business is not doing well at all. Its the second most important reason startups fail after the fact that they have run out of capital.
It would be best to have someone where you have different roles
Before you start having someone who has a different profile to you would probably be the best. For example if someone is more technical and the other person is not like a CTO and a COO the roles would be very clear to do and it would allow the investor to feel at ease about who they are investing in.
Going into business with someone you just met is very hard
Before you guys dont have any past relationship it will be very hard to go into business with someone you just met. When times get tough they may decide to do something else and leave. This is a massive red flag for any investor especially tier one investors so if you are going to choose a partner try to choose one you have already done something with.