Juniper M10i sufficient for BGP, or go with M20?

: I don't know much about Juniper but I'm about to learn
: with a new job.

If your experience is like mine, you'll fall in love with the M-series and absolutely despise the E-series (Unisphere)

: If I'm going to take full routes from a couple of upstreams
: and have a couple of peers will the M10i (768M max) be
: enough or is the M20 (2048M max) a better choice.

I use the M10i platform for some of my border routers. For example, below, I'm receiving full routes from a couple of upstreams and a partial with 768Meg for a good while now and no problems.

RE0> show chassis routing-engine
Routing Engine status:

    DRAM 768 MB
    Memory utilization 46 percent
    Model RE-5.0

RE0> show bgp summary
ASN #Active/Received/Damped
------ ----------------------------
AAA 625/994/0
BBB 152613/214987/0
CCC 62655/215400/0