I have 1 'hub' location that concentrates 4 'spoke' locations through 100 Mbps fiber-based leased lines. Each spoke has a 7200-NPE-G01 router.
I need to choose the equipment that will fit on the hub site. I don't know which one to choose between a 7300-NPE-G03 (for instance) or a Catalyst 6503.
Is the Catalyst 6503 a good choice ?
Insufficient information to really provide a good suggestion. 6503 is likely a good choice, although might not be optimal or best choice. Likewise so might a 7603, and as might a 7200 (with powerful enough engine) or 7304.
Four 100 Mbps WAN links can provide enough load that rules out ISRs, but besides 7200s, 7300s, 6500s or 7600s, LAN or MetroEthernet L3 switches might work very well for you too.
One major factor will be whether you need to provide a 100 Mbps fiber port, or ports. This because, most of the newer non-chassis L3 switches fiber ports only support gig. Other factors, for making a good choice, would be what features you need to support.
Well if ". . . 4 x Gigabit Ethernet ports." and "No real special feature is needed. "; and that's all you need, and also assuming copper ports, why the Cisco SD2005 5-port 10/100/1000 Gigabit Switch might be all you need.
Sorry, couldn't resist above, but with MetroEthernet, truly, such an unmanaged L2 switch might work, as would a 6503, so choice really depends on other feature needs, both hardware and software. Since you're already(?) using 7200s, I would guess you would want something better than the switch I just suggested, but I, or others, really can't provide good suggestions/recommendations without more information.
Just beware, if you're getting advice from anyone selling you the equipment, be aware there's often a conflict of interest.
BTW:, if there are 4 spokes, each with a dedicated link, wouldn't you want 5 ports? Here too I assume you want to connect to the hub network itself.
Jerry's note is an example of what can be suggested with more information.
With the C6500, you need to have a SIP/SPA to perform any kind of shaping. You might consider this if your Metro-E's CIR is not port speed.